Common Ringed Snake. 31 



consists of two layers, and meeting, as they do, by means of a median 

 aponeurosis, they must, in these animals which possess ribs of great 

 mobility, and no sternum, act to great advantage in propelling the 

 food which they swallow. Branches of the intercostal nerves are 

 seen passing over the homologue of the rectus abdominis along the 

 outer surface of the costal cartilages. Immediately above the line 

 occupied by this muscle are seen a series of muscular fasciculi 

 which arise from the tips of the ribs, and from the cartilages 

 at their junction with the ribs, and pass from behind and above, 

 forwards and downwards, to attach themselves to the lateral and 

 ventral rows of scales. More superiorly again we see a similar 

 row of muscles passing from an insertion on the ribs to an attach- 

 ment on the scales in such a direction as to decussate with that 

 of the first series. 



By the removal of the front wall of the right auricle a view is 

 obtained of the eyelid-like valve which guards the entrance of 

 the great veins into the auricle. The left auricle is very much 

 smaller than the right. The left superior cava is seen winding 

 over it. Between the two superior cavae we see the thyroid gland. 

 Anteriorly again we see the hyoid apparatus which is not connected 

 with the larynx, and consists of two long delicate bars of cartilage 

 which are free posteriorly, but anteriorly are connected with each 

 other by a fibrous commissure about on the level of the angle 

 of the lower jaw. The hyoglossi muscles, which make up a con- 

 siderable part of the general mass of the tongue, are seen to take 

 origin from the posterior portion and inner aspect of each hyoid 

 bar, and to enter the dark-coloured sheath in which the tongue 

 is lodged in front of the trachea. A large salivary gland is seen 

 to lie along the outer surface of both upper and lower jaw ; each 

 gland discharges its secretion by numerous ducts, which open 

 externally to the rows of teeth in each jaw. In the angle between 

 the eye and the superior maxillary gland we see the lacrymal 

 gland, which, like the other two just mentioned, is large in non- 

 venomous Snakes. 



Posteriorly to the liver a slip of blue paper has been placed 

 under the cystic duct just where it leaves the gallbladder and 

 passes down to join the hepatic duct. The ductus choledoehus 

 communis thus formed comes into relation with the pancreas, and 

 receives its ducts as it passes to empty itself into the duodenum. 



