Ix Introduction. 



developed. Glands which in Birds are only scantily developed 

 upon the cervical lymphatics, are not represented as distinct 

 from lymphatic plexuses, except by a mesenteric gland in the 

 Crocodilina. 



The trachea of the Loricata has a more perfect larynx than that 

 of the Squamata, and in some cases it describes a couple of convo- 

 lutions before entering the lungs. These organs differ in the Lori- 

 cata from those of other Reptiles in having, in correlation with 

 their non-transpirable integument, a much greater development of 

 internal parenchyma ; and in not projecting freely into the general 

 cavity of the body^ dissepimental processes of peritoneal membrane 

 separating them from it and foreshadowing thus, as also by their 

 possession of intrinsic muscular fibres^ the diaphragm of warm- 

 blooded animals. In the Srpiamata the lungs may be prolonged 

 in air-sacs, with little or no reticulation of vessels developed upon 

 them^ and these prolongations may be numerous as in Chamae- 

 leonoidea, or simple as in Ophidia. In some of the lower Lizards, 

 again^ as Hatteria, the lungs may be nearly as simple as those of 

 the Amphibia. The kidneys are situated posteriorly in the trunk, 

 and, except in the Ophidia, within the pelvic cavity, and close to 

 the cloaca. In the Crocodilina, indications of a separation of the 

 substance of the kidney into a cortical and medullary stratum are 

 not wanting. A urinary bladder is usually present in Sauria and 

 Cheloniaj but is absent in Ophidia and Crocodilina. In the Che- 

 Ionia, a sinus urogenitalis is present. The kidneys are not con- 

 formed to the sinuosities of the bony structures as in Birds. The 

 cerebral hemispheres are smaller relatively to the rest of the 

 encephalon, and to the spinal chord, than in Aves. The cerebral 

 hemispheres, corpora bigemina, and cerebellum, are larger in the 

 Loricata than in the Squamata. A tympanic cavity is present 

 except in Ophidia, Amphishaenoidea, and Hatteria. This latter 

 animal has the commencement of a spiral turn indicated in its 

 cochlea, which in other Reptiles is, as in Birds, merely a flask- 

 shaped cavity; but it differs both from Birds and from other 

 Reptiles in the absence of any intra- ocular structure corresponding 

 with the avian ' peeten,^ or the ' processus falciformis ' of other 

 Reptiles. 



Copulatory organs of two distinct types exist in the Loricata 

 and Squamata respectively ; those of the former division being 



