300 



REPTILIA. 



arrangement of which varies in different races. 

 It must be remembered that throughout the 

 entire class there is no diaphragm or other 

 septum dividing the viscera of circulation and 

 respiration from those of digestion, all being 

 inclosed in a common cavity, lined by the 

 pleuro-peritoneum, which gives off processes 

 to inclose and to fix them as far as is neces- 

 sary in their respective situations. In the tor- 

 toises, that portion of the mesentery which 

 attaches the small intestines, does not come 

 immediately from the vertebral column, and 

 only forms the mesentery after having fixed 

 the transverse colon by a meso-colon. This 

 remarkable disposition depends upon the ge- 

 neral arrangement of the pleuro-peritoneum, 

 and the extent of the cavities that it forms for 

 the lodgment of the lungs. The meso-rectum 

 also is derived rather from the lateral regions 

 of the pelvis than from its middle. There 

 are, besides hepato-gastric laminae, which pass 

 from the liver to the stomach, hepato-duodenal 

 laminae, between the liver and the duodenum ; 

 transverse gastro- colic laminae, which pass 

 from the stomach to the transverse portion of 

 the large intestine ; and duodeno-colic layers 

 connecting the duodenal loop with the as- 

 cending colon. On the right of the mesorec- 

 tum, there is an expansion which descends 

 from the dorsal portion of the abdominal 

 walls to join the proper mesentery. 



Lastly, the large intestine commences by a 

 loop which is bound down by peritoneal 

 laminae. 



In the Saurian reptiles, the mesentery is 

 well developed, that portion which is con- 

 nected with the large intestine, as well as that 

 which sustains the small intestine, coming off 

 from the vertebral column. There is no trans- 

 verse mesocolon. 



The pleuro-peritoneum of Ophidian reptiles 

 presents some varieties in its disposition. In 

 the Anguidae, a mesentery is given off from the 

 whole length of the front of the vertebral 

 column anteriorly : this serves to suspend the 

 ossophagus and stomach, furnishing likewise a 

 mesenteric fold to each lung, and to the liver. 

 After enveloping the liver it forms a suspen- 

 sory ligament attached to the mesial line of the 

 ventral aspect of the abdominal walls, so that 

 the whole may be regarded as forming two 

 bags connected together, both above and 

 below, along the middle line of the body, and 

 thus dividing the abdominal cavity into two 

 compartments by a vertical septum, extending 

 along its whole length. 



In the Ceciliae a similar disposition exists. 



In the true serpents the pleuro-peritoneum 

 forms a cell around the intestine, which con- 

 tains likewise small omental folds loaded with 

 fat : the intestine itself, moreover, is folded 

 into numerous festoons connected to each 

 other by fibro-cellular bands. The large 

 intestine in serpents has no connexion with 

 the stomach, or with the commencement of 

 the intestinal canal, as is almost invariably the 

 case in other vertebrata. 



Lymphatic System. The lymphatic vessels 

 in reptiles appear to be completely destitute of 



valves, except at the points where they ter- 

 minate in the veins; a circumstance which 

 explains the facility with which they can be 

 injected from trunk to branch. 



In the Chclonian reptiles the lymphatics of 

 the alimentary canal, especially those of the 

 stomach and small intestine, form two prin- 

 cipal layers, of which the inner one constitutes 

 a very delicate net-work *, so thin as only to be 

 well seen with a magnifying-glass, lying close 

 to the inner surface of the intestine, interlaced 

 amongst the blood-vessels, but easily distin- 

 guishable from their continuity. 



The external layer is made up of larger 

 branches, which are so numerous that they 

 touch each other, and after a successful injec- 

 tion completely cover the intestine : they all 

 affect a longitudinal direction, and have an 

 undulated or wavy appearance. 



The lymphatics of these two layers serve 

 to form another net-work placed external to 

 the last, made up of large confluent branches, 

 which convey the lymph into the principal 

 lacteal trunks of the mesentery, which latter 

 form a fourth net-work, the meshes of which 

 are very close and fine. 



In the urinary bladder and the oviduct, the 

 arrangement of the lymphatics is similar to 

 the above. 



In the lungs they form a superficial layer, 

 made up of large trunks ,- and a deep-seated 

 layer, composed of very fine branches. 



The external net-work of the gall-bladder 

 is made up of very small meshes ; whilst that of 

 the spleen, on the contrary, consists of large 

 confluent trunks, resembling sinuses : the latter 

 organ, however, has likewise a smaller deep- 

 seated set of lymphatic vessels which accom- 

 pany the ramification of the veins into its in- 

 terior. 



The lymphatics of the testicle have a ramified 

 or arborescent arrangement, increasing .in size 

 as they pass from the outer to the inner 

 margin of the organ, the branches forming 

 numerous anastomoses amongst themselves. 



The adipose tissue, situated between the 

 peritoneum and the carapax, is full of lym- 

 phatic vessels. Those of the peritoneum are 

 very small and numerous : their direction is 

 generally from before backwards. 



The liver seems to possess very few lym- 

 phatics, and these Panizza was unable to in- 

 ject, as also those of the oesophagus. 



Among the Saurian reptiles the lymphatics 

 have been examined in the Caiman, and in 

 several species of lizards. In the former, the 

 cloaca, the rectum, and the intestinal canal 

 inclose several net- works of lymphatic trunks, 

 the form and disposition of which varies. 

 There is one upon the inner surface, and ano- 

 ther upon the outer surface, the meshes of 

 which are very close, and the vessels much 

 convoluted. 



In the rectum, the lymphatics form two 

 layers, one superficial, the other deep-seated ; 

 in the former the vessels are large and their 



* Panizza Sopra il Sistema Linfatico dei Rettili, 

 &c. Pavia, 1833. in foL with six plates. 



