OCR Text |
Show 3 2 0 Mil. R. H. BURNE ON THE [Apr. 18, although to a certain extent trabecular in structure, consists practically of solid muscle. The ventricular septum is quite normal. . . The great vessels arise from the ventricle in the usual positions, but it is worth noting that the carotids, 7 cm. above their oiigm from the innominate artery, suddenly dilate to at least twice their original diameter and then very gradually narrow again towards the head. The arches of the two aortae are equal in size-2 cm. in diameter when flattened. They unite on a level with the apex of the ventricle. The cceliac artery arises from the left arch close to its union with the right, the mesenteric from the left side of the upper extremity of the abdominal aorta. The Veins. The Renal Portal System (text-fig. 72).-The chief affluent (text-fig. 72, il.v.) of the afferent renal vein is formed by the union of a number of small vessels upon the inner side of the ilium. The trunk thus formed runs forward to the hinder end of the kidney, and there divides into two branches-a dorsal one (the afferent renal vein) that runs upon the medio-ventral surface of the kidney, lateral to the ureter, and very soon becomes embedded in the kidney-substance; and a ventral branch that, after taking up the obturator vein, forms one of the roots of the anterior abdominal vein. The latter branch lies upon the dorsal surface of the intra-pelvic muscles, and appears upon the surface of the body-wall in the pubo-epipubic notch. Just in front of the epipubis it unites with its fellow of the opposite side, and the trunk formed by the union runs forward in the substance of the body-wall to the cleft between the ends of the coracoids. Here it receives vessels from the muscles of the left coracoid, then dips down towards the liver and enters it about the middle of the ventral surface of the left lobe. This is the left anterior abdominal vein. The light anterior abdominal vein is represented only by the small vessel formed by the union of the veins from the muscles of the right coracoid. It enters the posterior edge of the isthmus of the liver about its middle, in relatively the same position as the fully developed right anterior abdominal vein of Emys. The persistence of only one (the left) anterior abdominal vein, although normal in Amphibia and Lizards, is not the condition generally described as typical of Chelonia, in which (Testudo, Emys) both veins persist, forming right and left anterior abdominals. I notice, however, that Rathke* mentions that in young individuals of Chelone and in his specimen of Dermochelys the left anterior abdominal vein only is present. In Testudo grceca also '* Ratlike : Entwickl. p. 213. |