MAMMARY GLANDS IN MONOTREMATA. 765 



margin : the nasal cavity then extends backward, and terminates 

 immediately above the larynx, the tip of the epiglottis extending 

 into it, and resting upon the soft palate. 



On the middle line of the upper mandible and a little anterior 

 to the nostrils there is a minute fleshy eminence lodged in a slight 

 depression, fig. 601, b. In the smaller specimen this is surrounded 

 by a discontinuous margin of the epidermis, with which substance, 

 therefore, and probably (from the circumstance of its being shed) 

 thickened or horny, the caruncle had been covered. It is a 

 structure of which the upper mandible of the adult presents no 

 trace, and is obviously analogous to the horny knob which is 

 observed on the upper mandible in the foetus of aquatic and 

 gallinaceous Birds. I do not, however, conceive that this struc- 

 ture is necessarily indicative of the mandible's having been applied, 

 under the same circumstances, to overcome a resistance of pre- 

 cisely the same kind as that for which it is designed in the young 

 Birds which possess it. The shell-breaking knob is found in 

 only a part of the class ; and although the similar caruncle in the 

 Ornithorhynchus aifords a curious additional affinity to the Aves 

 precoces, yet, as all the known history of the ovum points strongly 

 to its ovo-viviparous development, the balance of evidence is still 

 in favour of the young being brought forth alive. 



The situation of the eyes, ib. c, was indicated by the conver- 

 gence of a few wrinkles to one point ; but when, even in the larger 

 of the two specimens, these were put upon the stretch, the in- 

 tegument was found entire, and completely shrouding or covering 

 the eyeball anteriorly. The fact is of importance to the question 

 of the mammiferous character of the Ornithorhynchus. For on 

 the supposition of the young animal possessing locomotive facul- 

 ties, which would enable it like the young gosling, immediately 

 after birth or exclusion, to follow the parent in the water, and 

 there to receive its nutriment (whether mucous or otherwise), the 

 sense of vision ought certainly to be granted to it in order to 

 direct its movements. The privation of this sense, on the con- 

 trary, implies a confinement to the nest, and a reception on land 

 of the mammary secretion of the parent. The auditory orifices, 

 ib. d, are situated about a line behind the eyes. The general 

 form of the body and the cartilaginous condition of the bones 

 of the extremities equally militate against the young Ornitho- 

 rhynchus possessing, at this period of its existence, active powers 

 of swimming or creeping. The head and tail are closely approxi- 

 mated on the ventral aspect, requiring force to pull the body out 

 into a straight line ; and the relative quantity of integument on 



