OCR Text |
Show 1880.] VARIATION IN E Q U U S ASINUS. 7 Canines long or short, sexual variation. Premolars : small " Wolves' teeth " occasionally present in front of four anterior molars. Stomach often presents a very marked central transverse constriction where cuticular mucous joins the villous. CcBcum sometimes retains the form it presents in eight months' foetus ; its apex sometimes very elongated and pointed. Colon.-Longitudinal muscular bands vary in size and in number at different parts of the bowel. Liver.-Lobes vary in form and much in size. Ligaments differ in degree of development, especially falciform ligament, which sometimes runs as far backwards as umbilicus, containing a pervious vein in its thin free margin. Parovarium.-On outer surface of broad uterine ligament, sometimes large, often obsolete. Male mammae often extremely large. Thyroid body varies much in form, especially in the size of the band connecting its lateral masses. Conchial carlilayes prolonged downwards by small rounded band to lateral part of guttural pouch and to posterior angle of stylohyal. A remarkable peritoneal band sometimes runs from the caecum to the omentum major, reminding us of a condition we have noted in one form of Macacus. ANGIOLOGY. Anterior aorta often entirely absent. Sometimes a large anterior mediastinal branch passes downwards from this vessel. The dorsal and posterior cervical vary in their relations to each other. Generally these vessels are united on the right side and distinct on the left; but this condition may be reversed. The cervical may become united by a well developed subcostal with the sixth costal as given off from the posterior aorta ; but this is not constant. The vertebral passes through or below the seventh cervical transverse process. The submaxillary may arise directly from the carotid instead of from the external carotid. External pectoral arises from internal pectoral, or axillary. Posterior aorta.-Bronchial and oesophageal often arise by common root, or are distinct. Renal may supply suprarenal capsules and kidney; or the former may be supplied directly by a branch from the posterior aorta. Spermatics-one sometimes considerably more anteriorly placed than the other, even given off by posterior mesenteric. Between internal iliacs occasionally a small middle sacral arises. The obturator, epigastric, and inguinal sometimes arise from external iliac. The origins of the profunda and of the artery of the cord often vary. The medullary artery of the femur is sometimes given off through the foramen at the anterior part of the bone instead of at the internal surface of the bone. The artery of the humerus is similarly variable. The circumflex of the toe is variously formed in different cases. Thus from these examples we see the arteries are the most fre- |