400 



MONOTREMATA. 



d 



The circumstances which first attract atten- 

 tion in these singular objects are the total ab- 

 sence of hair,* the soft flexible condition of 

 the mandibles, and the shortness of these parts 

 in proportion to their breadth as compared with 

 those of the adult. 



The integument Fig. 196. 



with which the man- 

 dibles are covered 

 is thinner than that 

 which covers the rest 

 of the body, and 

 smoother, present- 

 ing under the lens a 

 minutely granulated 

 surface when the 

 cuticle is removed, Head of young Ornithorhyn- 

 which, however, is chus - (Owen, Zool. Trans.) 

 extremely thin, and has none of the horny 

 character which the claws at this period present. 

 The margins of the upper beak are rounded, 

 smooth, thick, and fleshy; the whole of the 

 under mandible (fig. 196, g) is flexible, and 

 bends down upon the neck when the mouth 

 is attempted to be opened. The tongue, 

 (Jig. 196, /;,) which in the adult is lodged 

 far back in the mouth, advances in the 

 young animal close to the end of the lower 

 mandible; all the increase of the jaws beyond 

 the tip of the tongue, which in the adult gives 

 rise to a form of the mouth so ill calculated for 

 suction or application to a flattened surface, is 

 peculiar to that period, and consequently forms 

 no argument against the fitness of the animal 

 to receive the mammary secretion at an earlier 

 stage of existence. The breadth of the tongue 

 in the larger of the young specimens was 3 

 lines ; in the adult it is only one line broader; 

 and this disproportionate development is plainly 

 indicative of the importance of the organ to the 

 young animal, both in receiving and swallow- 

 ing its food. The mandibles are surrounded 

 at their base by a thin fold of integument, which 

 extends the angle of the mouth from the base 

 of the lower jaw to equal the breadth of the 

 base of the upper one, and must increase the 

 facility for receiving the milk ejected from the 

 mammary areola of the mother. The oblique 

 lines which characterize the sides of the lower 

 mandible in the adult were faintly visible on 

 the corresponding parts of the same jaw of the 

 young animal : a minute ridge of the inner 

 sides of these lines indicates the situations of 

 the anterior horny teeth of the adult. 



The situation of the exterior nostrils (figs. 

 195, 196, a) has already been given; they 

 communicate with the mouth by the foramina 

 incisiva, which are situated at nearly three lines 

 distance from the end of the upper mandible, 

 and are each guarded by a membranous fold 

 extending from their anterior margin : the nasal 

 cavity then extends backwards, and terminates 

 immediately above the larynx, the tip of the 



* This is not accidental, as in many of the adult 

 specimens sent over in spirit, for the cuticle is 

 entire. In the specimens which Mr. G. IJennett 

 discovered, the skin had a slight downy appear- 

 ance. 



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 de- 

 pression (7?g.l96, 6). In the smaller specimen 

 this is surrounded by a discontinuous margin 

 of the epidermis, with which substance, there- 

 fore, 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 structure 

 is necessarily indicative of the mandible's 

 having been applied, under the same circum- 

 stances, to overcome a resistance of precisely the 

 same kind as that for which it is designed in the 

 young Birds which possess it. The shell-break- 

 ing knob is found in only a part of the class; 

 and although the similar caruncle in the Orni- 

 thorhynchus affords a curious additional affinity 

 to the Aves altrices, yet, as all the known history 

 of the ovum points strongly to its ovo-vivipa- 

 rous development, the balance of evidence is 

 still in favour of the young being brought forth 

 alive. 



The situation of the eyes (fig. 195, b, 196, c) 

 was indicated by the convergence of a few wrin- 

 kles to one point; but when, even in the larger 

 of the two specimens, these were put upon the 

 stretch, the integument was found entire, and 

 completely shrouding or covering the eyeball 

 anteriorly. This fact is one of great importance 

 to the question of the mammiferous character 

 of the Ornithorhynchus. For on the supposition 

 of the young animal possessing locomotive 

 faculties, 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 



* Geoffroy St. Hilaire contending, in 1833, for 

 the analogy of the abdominal glands of the Orni- 

 thorhynchus with thosejof the Shrews which secrete 

 " a mucus possessing a very powerful odour," says, 

 " I should not be surprised, if this mucus, more 

 abundant and more substantial in the Monotremata, 

 became the nutriment of the young after their 

 hatching. The Monotremata would act, in this 

 respect, like some aquatic birds which conduct 

 their young after hatching to the water, and assist 

 them in their sustentation. The maternal instinct 

 would lead the female Ornithorhynchus to effect 

 the contraction of the gland, which is possible by 

 the efforts of the panniculus carnosus and the great 

 oblique muscle, between the fibres of which the 

 gland is seated, and thus procure for the young, 

 at several periods of the day, by way of nutri- 

 ment, an abundant supply of mucus. If this edu- 

 cation is carried on in the water, where we know, 

 by the history of the generation of frogs and the 

 nutrition of their tadpoles, that the mucus com- 

 bines with the ambient medium, becomes thick, 

 and supplies an excellent nutriment for the early 

 age of these reptiles, we shall understand the 

 utility of the ventral glands of the Ornithorhyn- 

 chus, as furnishing a source of nutriment for the 

 young of these animals, -for young Oripura newly 

 hatched." Gazette Medicate, Feb. 18th, 1833. 

 Proceedings Zool. Society, March 1833, p. 29. 



