CROCODILFANS, LIZARDS, AND SNAKES. 167 



somewhat recurved at the apex. It is obliquely truueate behind and 

 below. The inferior lace is excavated and the distal plane. There are 

 three tarsalia corresponding to tour external digits; the llrst digit 

 articulating directly with the astragalus, the second digit joins one tar- 

 sale, the third and fourth one, while the fifth digit is lacking. The fifth 

 tarsale is })roduced like a rudiuiental metatarsal. The three interior 

 digits only have uuguiform distal phalanges with corneous sheaths. [ 



Viscera. -The heart is situated in the anterior part of the body cav- 

 ity, and the lungs extend about half their length posterior to it. The 

 latter extend considerably cephalad of the bronchi, which enter at 

 about the posterior third of their length, at right angles to the axis of 

 the body. The liver is completely divided into right and left moie- 

 ties, each of which sends posteriorly a process of its external portion. 

 The alimentary canal is distinguished for the strong differentiation 

 of the stomach, which much exceeds anything known in the Sauria. 

 The cardium and pylorus are each small orifices, and the stomach has 

 a fundus at either end external and caudad to each. Toward the 

 pyloric fundus tlie walls are very thick with muscle. At its apex is a 

 siuall diverticulum in the ^1. mississiijpiensifi. The small intestine is of 

 relatively small diameter and the large intestine is large, and is not 

 distinguished into colon and rectum, and has no ciecum. The kidney 

 is coarsely lobate. 



The mesenteries are not so simple as in the Sauria, as they are less 

 less distinct from each other, and send branches in different directions. 

 The (I'sophagus has, besides the dorsal connection, connection with the 

 pericardium. The lungs are connected with both, and distally with 

 the cephalad surface of the liver. The liver has connection posteriorly 

 with all of these viscera, which is not muscular, but which represents 

 the dorsal part of the pericardium. A longitudinal fold connects the 

 pericardium with the two halves of the liver and the stomach, repre- 

 senting the gastrohepatic mesentery of the Sauria. From the caudad 

 margin of the liver on the right side a sheet extends to the body wall, 

 remaining free from the latter as far posteriorly as the kidney. A 

 corresponding slieet extends from the distal aspect of the stomach on 

 the right side. Both are connected with the body wall by bands and 

 threads. From each lobe of the liver near the median line a sheet 

 extends to the median body wall below, which is strongly muscular. 

 This is regarded as homologous with the inferior portion of the dia- 

 phragm of the mammals, and this with the posterior transverse hepato- 

 dorsal sheet may correspond with that structure. If so, the important 

 difference remains that in the alligator it includes the liver between 

 its two layers, while in the mammals it is entirely superior to the liver. 



The tympanic drum is deeply set beneath the superior postorbital 

 bar. It is protected by a fold of the integument which forms a fiap, 

 which is sus] tended from the postorbital bar, closing the orifice like a 

 lid. 



Geologic history. — The genus Alligator is oi much more modern origin 



