176 REPORT OF NATIONAL MUSEUM, 1898. 



Central canal of spinal cord present. The eye possesses the usual 

 character of the Mouocondylia in the presence of the pecten, which 

 extends from the choroidea to the sheath of the lens. It is not so 

 plicate as in birds. The organ of hearing conforms to the same type 

 in the absence of a helix and the presence of a lagena and sacculus. 

 The sympathetic nervous system is well developed and presents the 

 series of subvertebral ganglia. 



The alimentary canal is little specialized in the different parts of its 

 course, but the stomach is distinguished by its greater diaujcter and 

 generally more muscular walls. The diameter of the rectum generally 

 exceeds that of the preceding parts of the canal. Gall bladder and 

 pancreas present. Adipose bodies present. 



Heart with three chambers ; two auricles and one ventricle. The lat- 

 ter gives origin to a truncus communis arteriosus, which sends off one 

 or two aorta bows on each side, which combine to form a single aorta 

 root on each side, which fuse into the single aorta on the middle line 

 below the vertebral column. A sinus venosus. Posterior vena cava, 

 formed from the renal veins and traversing the liver after receiving 

 the portal vein. It is received, together with two jugulars, into the 

 sinus venosus. Posterior vertebral veins running below the ribs. 



Sexes distinct. Testis and vas deferens distinct from renal ducts, 

 discharging separately into cloaca. Males with two prehensile organs, 

 each inclosed in a sheath, one on each side of the base of the tail. 

 They are everted toward the cloaca! orifice when in use and are 

 retracted by invagination by the contraction of an axial muscle. They 

 are traversed by a groove, the sulcus spermaticus, which, beginning at 

 the base on the inner side, winds to the apex on the outer side, uniting 

 into a short, common vagina oi)ening into the cloaca from above to 

 receive the male prehensile organs. Oviducts distinct. The oviduct 

 consists of a tube, which, when not containing eggs, is collapsed, fall- 

 ing into numerous parallel, transverse folds. These folds are held in 

 place by an elastic band on each opposite border. The margin of the 

 fontanelle is of delicate membrane, and it is attached to the body wall 

 by a delicate fold of })eritoueum 



The integument is characteristically divided into small areas or 

 scales, by confluent inflections. These are occasionally the seat of 

 osseous deposit (Scincidtc, Gerrhonotidae), but this is exceptional. No 

 osseous scuta, other than the cases mentioned. This description 

 applies as well to the extinct Pythonomorj)ha as to the Sauria and 

 Ophidia. Abdominal scales generally different from the dorsal. 



The integument of the head is divided in many types into plates of 

 definite relations, which are homologous throughout the various sub- 

 divisions, and even between the suborders of Sauria and Ophidia. In 

 general, it may be believed that these plates have resulted from the 

 fusion of scales, both because scales are the primitive covering of the 

 body and are less si)ecialized than the head plates, but also because 



