Materials and Methods

Animals—The study involved 2 parts. For the first part (anatomic evaluation), cadavers were used of 3 boa constrictors (1 male and 2 females), 10 P curtus (3 males and 7 females), 4 Indian rock pythons (3 males and 1 female), and 6 ball pythons (3 males and 3 females). These 23 snakes had died from various causes, and their bodies had been stored at −20°C for a mean of 1 month.

For the second part (ultrasonographic evaluation), 46 privately owned boid snakes were used (16 ball pythons [7 males, 8 females, and 1 immature], 12 P curtus [5 males and 7 females], 10 Indian rock pythons [5 males, 4 females, and 1 immature], and 8 boa constrictors [4 males and 4 females]). Twenty of the live snakes (10 ball pythons, 4 P curtus, 3 Indian rock pythons, and 3 boa constrictors) were evaluated between July and September 2010, and 26 (6 ball pythons, 8 P curtus, 7 Indian rock pythons, and 5 boa constrictors) were evaluated in October and November of the same year. All live snakes were considered healthy on the basis of their medical history and physical examination findings. Last meal and reproductive status were recorded for each snake. This study was performed with approval of the Padua University Ethical Committee.

Anatomic evaluation—Snake cadavers were dissected prior to ultrasonographic evaluation of live snakes to overcome the lack of unambiguous anatomic references for the species in this study. All necropsy findings were carefully documented, and all coelomic organs (including major blood vessels) were identified and named in accordance with the most recent information on snake anatomy.^6–18 Photographs were obtained as part of this documentation.

Imaging procedures—Ultrasonographic examination of the coelomic cavity was performed on each snake by use of the same dorsolateral approach to probe placement. Each scan was performed with snakes positioned in ventral recumbency. Constant environmental temperature, set at 27°C, was maintained with a heater. Chemical restraint was not necessary; for the more aggressive subject, the head was kept inside a cotton sack to avoid injury to the snake or operator.

For each evaluation, ultrasonographic coupling gel was applied to the dorsolateral surfaces of the body and the tail. Images were obtained with a 6- to 10-MHz linear array transducer connected to a commercial sonographic scanner^a; a standoff pad was not used. The transducer frequency was adjusted throughout each examination to obtain the best imaging quality. In small subjects (ball pythons), the frequency was set at 10 MHz, whereas in large subjects (Indian rock pythons, boa constrictors, and P curtus), the frequency was set from 6 to 8 MHz. Each examination was completed within 15 to 30 minutes. All coelomic organs were evaluated in longitudinal and transverse scan planes. Findings are reported in the order of appearance during ultrasonography, starting at the tail.

Statistical analysis—Measurement values are reported as mean ± SD. The distribution of data regarding the anatomic structure measurements was tested for normality by means of graphic methods (histograms and Q-Q plots) and the Shapiro-Wilk test. When data were normally distributed, correlations between body weight or body length and thickness of the scent glands, colonic wall, gastric wall, and pyloric wall were evaluated by performing linear regression and calculating Pearson correlation coefficients (r). When data were not normally distributed, Spearman correlation coefficients (ρ) were calculated for nonnormally distributed values. All analyses were performed with commercially available software.^b Values of P < 0.05 were considered significant.

Results

A schematic drawing of the topographic anatomy of the coelomic organs was made on the basis of necropsy findings (Figure 1). The mean snout-to-vent length and body weight of the 46 live snakes were summarized (Table 1).

View Full Size

Schematic drawing of the topographic anatomy of the coelomic organs of snakes. L = Left.

Citation: American Journal of Veterinary Research 73, 5; 10.2460/ajvr.73.5.634

• Download Figure
• Download figure as PowerPoint slide

Scent glands and hemipenes—Paired scent glands were identified in all snakes examined (Figure 2). In male snakes, paired scent glands were visible ventral to the caudal vertebrae; paired hemipenes were located immediately ventral to the scent glands. In females, the scent glands were more prominent and occupied most of the cranial portion of the tail. In both sexes, the scent glands had a rough and non-homogeneous echotexture and a poor echogenicity. These glands had a lower echogenicity than the surrounding muscles. They appeared circular and surrounded by an echoic ring (the capsule) in transverse ultrasonographic scans and elongated and bordered by a well-defined capsule in longitudinal scans. An echoic muscular line was visible between the 2 scent glands in males and females.

View Full Size

Representative photographs (A–C) and ultrasonographic images (D and E) of the internal organs of boid snakes. A—Grossly dissected tail of a male boa constrictor. B and C—Cross sections (B is cranial to C) of the tail of a male Indian rock python (Python molurus molurus). D—Transverse ultrasonographic image of the tail of a male boa constrictor. E—Longitudinal ultrasonographic image of the tail of a male Python curtus. Inset—Muscles surrounding the hemipenes (arrowheads) and the hemipenis (arrow) are indicated. In all dissection photographs, the cranial aspect of the snake is to the left of the image, and the left side of the snake is oriented toward the top. In all cross section photographs, the left side of the snake is to the left; dorsal is oriented toward the top. In all transverse ultrasonographic images, the left side of the snake is to the left, and dorsal is toward the top. In all longitudinal ultrasonographic images, cranial is to the left, and the left side of the snake is toward the top. 1 = Left hemipenis. 2 = Right hemipenis. 3 = Left scent gland. 4 = Right scent gland. 5 = Vent. Cr = Cranial. Do = Dorsal. L = Left. Bar = 1 cm in ultrasonographic images.

Citation: American Journal of Veterinary Research 73, 5; 10.2460/ajvr.73.5.634

• Download Figure
• Download figure as PowerPoint slide

In males, the scent glands had a lower echogenicity and a rougher echotexture than did the hemipenes. Dimensions of the scent glands as measured just caudal to the vent in transverse images were summarized (Table 2). A significant positive correlation was detected between body weight and scent gland thickness (ρ = 0.29; P = 0.003) and between body length and scent gland thickness (ρ = 0.24; P = 0.003).

The hemipenes were easily identifiable in longitudinal scans of all male snakes but were less evident in transverse scans because of poorer contact between the body and the transducer consequent to the peculiar conformation of the tail. The hemipenes were visible in longitudinal scans as 2 echoic lines within 2 parallel anechoic lines (Figure 2). In transverse scan, the hemipenes appeared as 2 echoic circular structures positioned ventrally or laterally to the scent glands. The hemipenes consistently appeared considerably smaller than the scent glands.

Ureters, cloaca, and vagina—The cloaca was identified in all snakes immediately cranial to the vent (Figure 3). The cloacal wall was composed of 3 layers: an external hyperechoic layer, an anechoic or poorly echoic middle layer, and an internal hyperechoic layer. In transverse scans, the shape and the overall appearance of the cloacal wall varied with the cloacal content. In snakes in which it was full of urine and feces, the cloaca appeared round with a thin smooth wall, whereas in snakes with a cloaca containing a limited amount of fluid, its wall appeared thicker and irregular. In longitudinal scans, the almost constant presence of fluids in the cloaca provided optimal organ visibility.

View Full Size

Representative photographs (A–C) and ultrasonographic images (D–H) of the internal organs of boid snakes. A—Grossly dissected female ball python (Python regius) after removal of the fat bodies of the cloaca. B—Gross anatomic dissection after removal of the fat bodies of the cloaca of a male boa constrictor. C—Cross section of the cloaca of a male Indian rock python. D—Transverse ultrasonographic image of the cloaca (distended with urine) of a female Indian rock python. Inset—External hyperechoic layers (arrowheads) and internal hypoechoic layer (arrow) of the cloacal wall. E—Transverse ultrasonographic image of the cloaca (empty) of a female ball python. F—Longitudinal ultrasonographic image of the cloaca of a male ball python. Feces are evident in this snake (asterisk). G—Detail of the ureter. H—Transverse ultrasonographic image of the cloaca and vagina of a female ball python. 1 = Left oviduct. 2 = Right oviduct. 3 = Left vagina. 4 = Right vagina. 5 = Ureter. 6 = Deferent duct. 7 = Urodeum. 8 = Coprodeum. See Figure 2 for remainder of key.

Citation: American Journal of Veterinary Research 73, 5; 10.2460/ajvr.73.5.634

• Download Figure
• Download figure as PowerPoint slide

The ureters were identified in the cloacal tracts in 2 male ball pythons and 4 Indian rock pythons (2 males and 2 females) only through transverse scans; peristaltic activity was always evident (Figure 3). The vagina was identified ventral to the cloaca in 4 female ball pythons, 3 female P curtus, and 1 female boa constrictor. The vagina was seen only through transverse scans. The ultrasonographic appearance of the vagina was a figure-8–shaped, thick-walled hollow organ immediately ventral to the colon. No interspecies differences were evident in the ultrasonographic appearance of the cloaca.

Colon and cecum—The junction between the small and large intestine was easily identified in all P curtus, Indian rock pythons, and boa constrictors because of the presence of a well-developed cecum that was located beside the terminal portion of the small intestine (Figure 4). No transition in intestinal wall thickness was observed at the junction between small and large intestine. The wall of the colon and cecum appeared similar to that of the cloaca. Only small portions of that wall were clearly visible in most snakes because of the constant presence of gas within the lumen. The amount of gas and fluid appeared to be related to digestive status; snakes fed during the week preceding the examination had a higher fluid content in the colon, whereas snakes from which food had been withheld for more than a week previously had higher amounts of intestinal gas.

View Full Size

Representative photographs (A-D) and ultrasonographic images (E–H) of the internal organs of boid snakes. A, B, and C—Gross anatomic dissection after removal of the fat bodies at the junction between small and large intestine of a male boa constrictor (A), female ball python (B), and female P curtus (C). D—Cross section of the small-large intestine junction of a male Indian rock python. E—Longitudinal ultrasonographic image of the left kidney of a male Indian rock python. F—Transverse ultrasonographic image of the small-large intestine junction of a male Indian rock python. G—Transverse ultrasonographic image of the left kidney and colon of a male ball python from which food had been withheld. H—Transverse ultrasonographic image of the large intestine of a recently fed female boa constrictor. 1 = Small intestine. 2 = Cecum. 3 = Large intestine. 4 = Right kidney. 5 = Left kidney. 6 = Right ureter. 7 = Right deferent duct. 8 = Renal efferent vein. 9 = Left ovary. 10 = Right ovary. 11 = Left oviduct. 12 = Right oviduct. See Figure 2 for remainder of key.

Citation: American Journal of Veterinary Research 73, 5; 10.2460/ajvr.73.5.634

• Download Figure
• Download figure as PowerPoint slide

The distinction between the small and large intestine was less evident in ball pythons than in the other species because of the absence of the cecum and the straight aspect of the intestinal tract. A significant positive correlation was evident between body weight and colonic wall thickness (ρ = 0.20; P = 0.035) as well as between body length and colonic wall thickness (ρ = 0.23; P = 0.018).

Kidneys—The kidneys were identified in all snakes examined. In all snakes, the left kidney was seen just cranial to the cloaca, whereas the right kidney was located cranial to the left kidney (Figure 4). In some snakes, the cranial pole of the left kidney and the caudal pole of the right were visible in the same transverse scan. The echogenicity of the kidneys was similar to that of the fat bodies (particularly in ball pythons and Indian rock pythons), making the identification of the kidneys challenging. In transverse scans, the kidneys ranged in appearance from triangular to nearly oval, with a fine echotexture similar to that of the mammalian renal cortex. The ureter could be traced starting from the cranial pole of the kidney and running medially to the ventral surface of the organ; it was often visible as a round structure with a hyperechoic wall. The renal efferent vein was also visible sometimes lateral and sometimes medial to the ureter. In longitudinal scans, the renal lobules were sometimes visible as multiple hyperechoic lines, whereas all the other renal structures were difficult to identify.

Gonads—Snakes evaluated between July and September had fewer and smaller follicles than those evaluated between October and November (Figures 5 and 6). In the snakes evaluated in the summer, follicle identification was sometimes challenging. Snakes evaluated during October and November had well-developed follicles in the dorsal portion of the coelomic cavity just cranial to or at the same level of the corresponding kidney, depending on the stage of the ovarian cycle. The follicles appeared as multiple round anechoic structures surrounded by a 2-layered wall; the inner layer appeared as echoic, whereas the outer layer was anechoic. The ovarian parenchyma was not visible. The ovaries appeared loosely connected to the coelomic cavity; for this reason, they appeared sometimes medial and sometimes lateral to the kidneys. In ovulating snakes, the left ovary extended from the stomach to the caudal pole of the left kidney, whereas the right extended from the pylorus to the caudal pole of the right kidney. The right ovary was cranial to the left. Different intermediate phases of ovulation were visible in scanned animals, but an accurate description of the ultrasonographic appearance of the ovarian cycle of the boid snakes was beyond the purpose of this study.

View Full Size

Representative photographs (A and B) and ultrasonographic images (C and D) of the internal organs of boid snakes. A—Detail of the right ovary (fat bodies removed) of a grossly dissected female ball python that died in July (sexual resting season). B—Longitudinal ultrasonographic image of developing follicles of a P curtus. C—Cross section of the oviduct of a gravid female boa constrictor. D—Transverse ultrasonographic image of the oviduct of a gravid female boa constrictor. 1 = Ovary. 2 = Oviduct. 3 = Eggs. 4 = Small intestine. See Figure 2 for remainder of key.

Citation: American Journal of Veterinary Research 73, 5; 10.2460/ajvr.73.5.634

• Download Figure
• Download figure as PowerPoint slide

View Full Size

Representative photographs (A and B) and ultrasonographic image (C) of the internal organs of boid snakes. A—Detail of the testes (fat bodies removed) of a grossly dissected male boa constrictor that died in June (sexual resting season). B—Cross section of the small intestine and right testis of a Indian rock python that died in July (sexual resting season). C—Transverse ultrasonographic image (acquired in November [mating season]) of the right testis and small intestine of an Indian rock python. 1 = Right testis. 2 = Right deferent duct. 3 = Left testis. 4 = Left deferent duct. 5 = Small intestine. 6 = Right kidney. 7 = Left renal efferent vein. 8 = Right renal efferent vein. 9 = Posterior vena cava. 10 = Dorsal aorta. 11 = Fat body. See Figure 2 for remainder of key.

Citation: American Journal of Veterinary Research 73, 5; 10.2460/ajvr.73.5.634

• Download Figure
• Download figure as PowerPoint slide

The deferent duct in males and the oviduct in females were visible lateral to the ureter and as a small tubular structure with a highly echoic wall. The ultrasonographic characteristics of the oviducts varied widely as a function of reproductive status. In all nongravid snakes, the oviducts were visible only in the tract medial to the kidneys. The remaining portion of the oviducts was visible only in gravid snakes.

Paired testes, lying on the dorsal aspect of the coelomic cavity just cranial to the cranial pole of the kidneys, were identified in all sexually mature male snakes (Figure 6). Those evaluated in October and November had noticeably larger testes than those evaluated between July and September. In snakes evaluated in the summer, the cranial pole of the right testis extended to the stomach, whereas the caudal pole overlapped the cranial pole of the left testis. In transverse scans, the testes appeared oval to round; in longitudinal scans, they appeared elongated. The testes had a fine echotexture similar to that of the fat bodies but with a lower echogenicity. In transverse scans, the deferent duct and the renal efferent vein were visible medial to the testis (the deferent duct was lateral and the vein was medial). Color Doppler ultrasonography was used for the differentiation of the renal efferent vein from the deferent duct; no flow was observed in the deferent duct. In snakes evaluated in October and November, the deferent duct and the renal efferent vein were dorsal to the testis, presumably as a result of testicular enlargement.

Small intestine—The small intestine was identified in all snakes. The small intestine in snakes from which food had been withheld ranged from completely rectilinear (ball pythons; Figure 7) to highly convoluted in the proximal portion of the tract and rectilinear in the distal portion (boa constrictors and Indian rock pythons). The small intestine had few similarities to that of mammals; the typical stratification recognized in mammalians was not appreciable. Only 2 layers could be identified: a thin, external anechoic-hypoechoic layer (the tunica muscularis) and a thick, nonhomogeneous, internal echoic layer (the mucosa). In longitudinal scans, the structures of the intestine became more evident than in transverse scans and the loops could be easily identified. Although an accurate description of the ultrasonographic intestinal changes related to feeding and food withholding were beyond the scope of the present study, it was apparent that the intestinal mucosa of recently fed snakes was thicker than that of snakes from which food had been withheld.

View Full Size

Representative photographs (A–D) and ultrasonographic images (E–H) of the internal organs of boid snakes. A, B, and C—Grossly dissected female ball python (A), male boa constrictor (B), and male P curtus (C), with fat bodies removed to show the small intestine. D—Cross section of the small intestine of a male Indian rock python. E—Transverse ultrasonographic image of the intestine of a female boa constrictor from which food had been withheld. F—Longitudinal ultrasonographic image of the intestine of a male boa constrictor from which food had been withheld. G—Longitudinal ultrasonographic image of the intestine of a recently fed female boa constrictor. Inset—External hypoechoic layer (arrowhead) and internal nonhomogeneous layer (arrow) of the small intestine wall. H—Transverse ultrasonographic image of the intestine of a recently fed male boa constrictor. 1 = Small intestine. 2 = Cecum. 3 = Large intestine. 4 = Stomach. 5 = Right testis. 6 = Left testis. 7 = Left deferent duct. 8 = Right renal efferent vein. 9 = Aorta. 10 = Left renal efferent vein. 11 = Right kidney. 12 = Hepatic vein. 13 = Right ovary. 14 = Fat body. See Figure 2 for remainder of key.

Citation: American Journal of Veterinary Research 73, 5; 10.2460/ajvr.73.5.634

• Download Figure
• Download figure as PowerPoint slide

Gallbladder—The gallbladder was visible in all snakes when a left lateral approach to probe placement was used to overcome the distal shadowing artifact caused by the caudal portion of the right lung (Figure 8). The gallbladder was separated from the liver and located ventrolateral to the pylorus, pancreas, and spleen. It appeared oval in shape, with its long axis parallel to the midline in all snakes examined. Small amounts of echogenic, nonshadowing, suspended material were present in 36 of the 46 snakes; no interspecies differences were evident.

View Full Size

Representative photographs (A–D) and ultrasonographic image (E–H) of the internal organs of boid snakes. A—Grossly dissected male boa constrictor (fat bodies partially removed) showing the pyloric region. B—Detail of the pylorus, spleen, pancreas, and gallbladder of a grossly dissected male boa constrictor. C—Cross section at spleen level of a male Indian rock python. D—Cross section at the gallbladder-pancreas level of a male Indian rock python. E—Transverse ultrasonographic image of the spleen of a female boa constrictor. F—Transverse ultrasonographic image of the pancreas of a female boa constrictor. G—Transverse ultrasonographic image of the pancreas of a female Indian rock python. H—Transverse ultrasonographic image of the pancreas, gallbladder, and pylorus of a male boa constrictor. 1 = Stomach. 2 = Pylorus. 3 = Spleen. 4 = Gallbladder. 5 = Pancreas. 6 = Small intestine. 7 = Fat body. See Figure 2 for remainder of key.

Citation: American Journal of Veterinary Research 73, 5; 10.2460/ajvr.73.5.634

• Download Figure
• Download figure as PowerPoint slide

Pancreas—The pancreas was identified medial to the gallbladder and caudal to the spleen in all snakes (Figure 8). The echotexture of the parenchyma was coarse and more hypoechoic than the surrounding structures (fat bodies). No interspecies differences were detected in the pancreatic echogenicity and echotexture. In ball pythons, P curtus, and boa constrictors, the shape of the pancreas was almost round in longitudinal and transverse scans. It was elongated in transverse scans and round in longitudinal scans involving Indian rock pythons. No differences between recently fed snakes and snakes from which food had been withheld were noticed.

Spleen—The spleen could be identified in only 2 Indian rock pythons (1 male and 1 female) and 2 female boa constrictors (Figure 8). Identification of the spleen was challenging; gas inside the stomach or the small size of the organ limited visibility. In our experience, the spleen was best identified in transverse scans when moving the transducer craniolaterally, starting from the pancreas. The resulting echogenicity of the spleen was lower than that of the pancreas. Splenic echotexture resembled that of a mammalian lymph node except for the presence of multiple hyperechoic lines (the perilymphoid fibrous zone), giving the organ a honeycomb appearance. The spleen appeared round and firmly secured to the pancreas in transverse and longitudinal scans.

Stomach, pylorus, and esophagus—The stomach was visible in all snakes when a left lateral approach was used (Figures 8, 9 and 10). The pylorus was easily identifiable medial and dorsal to the gallbladder. Remarkable interspecies differences were noticed in the shape of the stomach; in ball pythons, Indian rock pythons, and boa constrictors, the stomach was saccular, located within the left side of the coelomic cavity and with its long axis parallel to body midline. On the other hand, in P curtus, the stomach had a more convoluted shape than in the other species. The distinction between stomach and pylorus was more evident in P curtus as well.

View Full Size

Representative photographs (A–D) and ultrasonographic images (E – G) of the internal organs of boid snakes. A—Grossly dissected male boa constrictor (fat bodies removed) showing the external appearance of the stomach. B—Internal aspect of the stomach of the same snake as in panel A. C—Grossly dissected (fat bodies removed) female P curtus showing the external appearance of the stomach. D—Cross section of the stomach of a male Indian rock python. E—Transverse ultrasonographic image of the stomach of a male P curtus. Inset—External echoic layer (arrowhead) and internal anechoic layer (arrow) of the stomach. F—Longitudinal ultrasonographic image of the stomach of a female boa constrictor. G—Longitudinal ultrasonographic image of the stomach of a male P curtus. 1 = Stomach. See Figure 2 for remainder of key.

Citation: American Journal of Veterinary Research 73, 5; 10.2460/ajvr.73.5.634

• Download Figure
• Download figure as PowerPoint slide

View Full Size

Representative photographs (A and B) and ultrasonographic image (C) of the internal organs of boid snakes. A—Grossly dissected male boa constrictor showing the lungs and liver. B—Cross section of the lungs and liver of a male Indian rock python. C—Transverse ultrasonographic image of the liver and esophagus of a male P curtus. Inset—External echoic layer and internal anechoic layer (arrowhead) of the esophagus. 1 = Liver. 2 = Esophagus. 3 = Left lung. 4 = Right lung. 5 = Hepatic vein. 6 = Caudal vena cava. 7 = Aorta. See Figure 2 for remainder of key.

Citation: American Journal of Veterinary Research 73, 5; 10.2460/ajvr.73.5.634

• Download Figure
• Download figure as PowerPoint slide

The stomach and pyloric wall had only 2 layers: a thin external echoic layer and a thick internal anechoic layer. Gastric folds were quite evident both in longitudinal and transverse scans. Snakes lacked cardias. Significant positive correlations were detected between body weight and gastric wall thickness (r = 0.31; P = 0.002) and body length and gastric wall thickness (r = 0.32; P < 0.001). Moreover, a significant positive correlation was detected between body weight and pyloric wall thickness (r = 0.17; P = 0.024) and body length and pyloric wall thickness (r = 0.22; P = 0.091).

The esophagus (Figure 10) was visible only in transverse scans in 3 ball pythons (1 male and 2 females), 3 female P curtus, 4 Indian rock pythons (3 males and 1 female), and 1 male boa constrictor. The precardiac tract of the esophagus was difficult to see, likely because of the thin wall and the absence of internal material in healthy snakes. The postcardiac tract of the esophagus could be identified in some snakes, but the concurrent presence of the lungs and the intrinsic mobility of the organs made its identification somewhat difficult. The esophagus appeared round with its wall comprised of 2 concentric layers: an external echoic and internal anechoic layer.

Liver—In most snakes, the liver was identified in the second third of the snake body when a ventral approach to probe placement was used (Figure 10). The liver had a mammalian-like echotexture, but echogenicity could not be compared with adjacent organs as in mammals because neither fat bodies nor parenchymal organs were present in this region. Small round structures with hyperechoic walls, resembling mammalian portal vessels, were often visible in the parenchyma. Both the caudal vena cava running on the ventral surface of the liver and the hepatic vein on the dorsal surface were visible in all snakes. In transverse scans, the liver appeared oval in shape; a hyperechoic line was visible on the medial surface of the liver at the interface between liver and lungs. In longitudinal scans, the liver appeared as a straight parenchymal organ with an even border in all snakes.

Coelomic cavity and fat bodies—Fat bodies occupying the ventral part of the coelomic cavity except for the lung and neck regions were visible in all snakes, showing a similar distribution throughout the body of the species examined (Figures 5–7). Fat bodies had a higher echogenicity than the surrounding parenchyma and a fine echotexture. All P curtus had large fat bodies, compared with fat bodies in the other species examined. Small amounts of free fluid within the coelomic cavity were identified in 1 male ball python, 3 female P curtus, 1 male boa constrictor, and 1 female boa constrictor.

Discussion

The existing literature on ultrasonographic examination of boa constrictors proposes a ventral approach to probe placement to overcome shadowing artifact produced by the ribs.⁵ In the study reported here, a dorsolateral approach to probe placement was used to scan most coelomic organs (only the liver and the vagina required a ventral approach because of shadowing produced by the lungs for the liver and by the colon for the vagina). In our opinion, a ventral approach leads to 2 problems. For one thing, that approach is uncomfortable for snakes and so chemical restraint becomes necessary. For another, the fat bodies present, mostly in the ventral aspect of the coelomic cavity, reduce image quality (particularly in large snakes). The heart was not evaluated because comprehensive reports^19,20 of echocardiographic findings in snakes already exist.

The results of the present study suggested that a complete ultrasonographic examination of the coelomic cavity of boa constrictors, P curtus, ball pythons, and Indian rock pythons can be easily performed and that ultrasonography can be used as a routine diagnostic tool in these species. Although the ability to use ultrasonography in the evaluation of reptilian species is considered important,^21,22 the large number of these species and the lack of references hinder provision of high-quality veterinary services in reptile medicine. We believe the diagnosis of many diseases of snakes, such as egg retention, abscesses, tumors, gastroenteritis, renal diseases, and intestinal occlusions, could be improved by the standardization of an ultrasonographic technique.

Statistical analysis revealed significant positive correlations between the diameters and thickness of scent glands, gastric and pyloric walls, and colonic wall with body weight and body length in the present study. Moreover, as a consequence of the small intraspecific variation (SD) in the thickness of the colonic, gastric, and pyloric walls among examined snakes, we propose that the values reported here (Table 2) can be used as reference values for those species.

Comparison of the present findings with existing literature² on typical ultrasonographic findings in green iguanas reveals some similarities. Seasonal changes exist in the morphology and topography of the gonads, particularly the interposition of the testes and ovaries between the pylorus and the coelomic wall during the breeding season, and in pyloric and gastric wall layering. The seasonal changes of the dimensions of the gonads described here pertain to captive snakes. For most reptiles (particularly temperate species), reproductive behavior commences in spring after a seasonal cooling.²³ Tropical boid snakes such as boas and pythons usually breed during the cooler seasons.²⁴ It is therefore possible that the seasonal changes of the gonads could differ among snakes living at different latitudes. For captive snakes, environmental conditions are largely controlled by the owners and the breeding season can be modified by controlling the environmental temperature.²²

The findings reported here may not pertain to the ultrasonographic features of the coelomic organs of other snake species. These features could also differ from those of snakes that live in the wild as a result of a more varied diet, different habitat, and greater genetic variation.