XIII 



PHYLUM CHORDATA 



311 



marking the position of the ova. They are situated a little further 



back than the testes, and each is attached to the body-wall by a 



fold of the peritoneum, the meso- 



arium (ms. o.). The oviducts (od.) 



are thin-walled, wide, plaited tubes 



which open in front into the cavity 



of the body (od'.), while behind 



they open into the posterior part of 



the cloaca, their opening (od".) 



being distinct from, and a little in 



front of, those of the ureters. A 



fold of the peritoneum, the broad 



ligament (b. lg.), attaches the oviduct 



to the body -wall. 



2. DISTINCTIVE CHARACTERS AND 

 CLASSIFICATION. 



The Reptilia are cold-blooded 

 Craniata with a horny epidermal 

 skeleton of scales, and frequently 

 with an armour of dermal bony 

 plates. The centra of the verte- 

 brae have spheroidal articular sur- 

 faces. There are usually only two 

 vertebrae in the sacral region. The 

 episternurn, when present, always 

 remains distinct from the clavicles. 

 The floor of the acetabulum is 

 often completely ossified. The pubes 

 and the ischia usually meet in 

 ventral symphyses. The meta- 

 tarsals do not become ankylosed. 

 The mandible very usually bears 

 teeth. The optic lobes are situated 

 on the dorsal aspect of the brain. 

 The ventricle is rarely divided by a 

 are always two aortic arches in the 



od 



FIG. 921. Female urinogenital organs of 

 JLacerta viridis. The ventral Wall 

 of the cloaca, the urinary bladder, the 

 posterior end of the left oviduct, and 

 the peritoneal investment of the left 

 ovary and oviduct are removed. b. Ig. 

 broad ligament ; cl. 1 anterior, and cl.v 

 posterior divisions of the cloaca ; k. 

 kidney ; ms. o. mesoarium ; od. left 

 oviduct ; od'. its peritoneal aperture ; 

 od". aperture of right oviduct into the 

 cloaca ; ov. ovary ; ur. aperture of 

 ureter. (From Parker's Zootomy.) 



complete partition, 

 adult. 



There 



ORDER I. SQUAMATA. 



Reptilia in which the surface is covered with horny epidermal 

 scales, sometimes with the addition of dermal ossifications. The 

 opening of the cloaca is transverse in direction. There is a pair 

 of eversible copulatory sacs in the male. The vertebrae are nearly 

 always procoelous. The sacrum, absent in the Ophidia and 

 Bythonomorpha, consists of two vertebrae in the Lacertilia. The 



