316 



KEPTILIA. 



membrane, which is the middle tunic of the 

 eyelid. This is very delicate and soft, and 

 perfectly transparent in the centre, but to- 



Fig. 232. 



Diagram of the Conjunctiva of a Serpent. (After 

 Cloquet.} 



a, eye-ball ; b, optic nerve ; c, eyelid ; d, skin ; e e, 

 f, conjunctiva. 



wards its circumference it encloses some 

 opaque whitish fibres, supposed by Cloquet to 

 be muscular. This layer, at the margin of the 

 orbit, is manifestly continuous with the dermis: 

 internally it is lined by the third layer, which 

 is mucous, being in fact the membrana con- 

 junctiva, which is reflected on to it from the 

 surface of the eye-ball. 



All around the circumference of the eyelid 

 there is a whitish, granular, transparent sub- 

 stance, the nature of which is apparently 

 glandular. 



The lachrymal apparatus in serpents consists 

 of a lachrymal gland ; of a mucous sac formed 

 by the conjunctiva, into which the secretion of 

 the lachrymal gland is poured ; of an excretory 

 duct, or lachrymal canal ; and moreover of a 

 large and tortuous cavity, which receives the 

 tears and transmits them into the mouth. 



The lachrymal gland is proportionally of 

 very great size, and is situated behind the eye 

 and the post-orbital ligament. By its an- 

 terior surface, which is concave, it adheres to 

 the conjunctiva by means of its numerous 

 small excretory ducts. This gland is enclosed 

 in a very delicate cellular capsule. It is 

 made up of rounded whitish granules united 

 together by numerous vessels and nerves. 



The conjunctiva lines not only the internal 

 surface of the eyelid, but also a large portion 

 of the cavity of the orbit, from which it is re- 

 flected on to the front of the eye-ball, thus 

 forming a complete sac without any opening 

 externally (fig. 232, /). On the anterior part 

 of the floor of this sac there is a single pore, 

 large enough to admit a hog's bristle. This 

 is the punctum lachrymale, which is single like 

 the eyelid, behind and beneath which it is 

 situated : the punctum leads into a very deli- 

 cate membranous tube, which constitutes the 

 lachrymal canal. This latter passes down- 

 wards and forwards, enters an infundibular 

 channel in the lachrymal bone, and passing 

 through this, arrives at the external wall of 

 the nasal fossa, with which, however, it does 

 not communicate, but passes on to open into 

 a wide tortuous cavity, named by Cloquet 

 the intermaxillary sac. 



Urinary Apparatus. The arrangement of 

 the urinary apparatus is very similar through- 

 out all the oviparous vertebrata. The kidneys 

 are invariably situated very far back in the 

 abdominal cavity, where they are suspended 

 beneath the spine. They are distinguished 

 from the same glands in mammalia by the 

 circumstance of their presenting no division 

 into cortical and medullary portions, and by 

 the total absence internally of any pelvis or 

 infundibulum, their whole substance seeming 

 to be made up of convoluted caecal tubes. 



They vary slightly in the different orders in 

 their form and relative size, the principal 

 differences worthy of notice. In Chelonian 

 order they are short, oval masses, of a some- 

 what prismatic shape, or else, as in the turtle 

 (Testudo caretta), they are flat and triangu- 

 lar. Examined superficially, they have the 

 appearance of being divided into numerous 

 lobules, so that their surface has a convoluted 

 appearance, somewhat like that of the human 

 brain ; but towards the centre of the organ, 

 this lobulated structure is not distinguishable. 

 They are situated very far back, occupying 

 a very considerable space in the pelvic region. 



In the Saurians likewise, the kidneys seem 

 externally to be more or less divided into 

 lobules; they are generally almost entirely 

 contained in the cavity of the pelvis, where 

 they are placed side by side beneath the arch 

 of the sacrum, extending backwards even to 

 beneath the tail, so that they are situated 

 immediately above the cloaca. Their shape 

 is also more elongated than in the preceding 

 order. 



In the Ophidian reptiles the kidneys are 

 much elongated, so as to adapt them to the 

 slender shape of the body of the animals ; and 

 they are composed of distinct lobes placed 

 one before the other, and connected loosely 

 together, so as not to interfere with the 

 flexibility of the body. For the same reason 

 the two kidneys are not placed upon the 

 same level, but the right is situated con- 

 siderably farther forward than the left ; they 

 are, moreover, only loosely connected with the 

 spine by broad processes of peritoneum, in 

 which they are enveloped ; an arrangement 

 which leaves the movements of the spinal 

 column perfectly free. 



The kidneys of the reptilia seem to be en- 

 tirely made up of convoluted uriniferous 

 tubes, which as they issue from the different 

 lobes unite successively to form a common 

 duct, which runs along the external border of 

 the organ, and constitutes the ureter. The 

 common trunks of these urinary canals occu- 

 py the fissures between the different lobes of 

 the kidneys, in each of which they divide very 

 regularly as they diverge, so that their rami- 

 fications have a pyriform appearance ( fig. 233, 

 .). 



In the embryo and in very young reptiles 

 the kidneys seem to be made up of pyriform 

 vesicles which are arranged transversely, 

 their pedicles terminating at right angles in 

 the ureter ; or else they are made of simple 

 tubes disposed in a similar manner. The 



