ORNITHORHYNCHUS. 



ORNITHORHYNCHUS. 



126 



In both of the Monotremes the most remarkable part of their 

 osteology is perhaps the shoulder, which answers to that of birds, and 

 still more to that of certain lizards. The external surface of the 

 scapula is concave, so that it is far from adapting itself to the ribs. 

 Its form and relative position will be better explained by the cuts than 

 by words. The whole- of what may be termed the sternal apparatus 

 appears to be formed more after the model of the Saurian* than after 

 that of the Mammals; indeed it very much resembles that of the 

 Ichthyosaurus [ICHTHYOSAURUS], and, like it, is admirably adapted for 

 an animal destined to collect its food at the bottom of lakes and 

 rivers, and requiring machinery to enable it to rise continually to the 

 surface for a supply of air. 



Sternal apparatus of Ornitkorhynchus, two-thirds of the natural size. 



The bones of the arm and fore arm, &c., have nothing so remarkable 

 about them as to require particular description, especially as their 

 conformation and relative position will be seen below; but it is 

 deserving of notice that the carpus reminds the observer of the same 

 part in the Carnitora. The number of the phalanges is the same as 

 in the other mammals, two for the thumb and three for the fingers. 



The pelvis and posterior limbs of the Monotremes are framed more 

 according to the Marsupial type ; and the animal presents the super- 

 numerary bones which are articulated to the pubis and embedded in 

 the muscles of the abdomen, and are characteristic of that group. 

 Their locality is the same and they are as well developed as in the 

 Opossum. [MABSUPIATA.] They are remarkable for the width of 

 their base, which occupies nearly the whole of the anterior border of 

 the pubis. But besides these marsupial bones there are in the external 

 part of the pubis of the Ornithorhynchus two external pointed apo- 

 physes, one directed outwards, the other forwards. The ossa ilii are 

 short, prismatic, and a little enlarged on their anterior border ; the 

 pointed tuberosities of the ossa ischii are directed backwards, and the 

 ischium itself is not soldered to the sacrum as in the other Kdentata ; 

 the three bones join as usual at the cotyloid fossa, but it is to be 

 remarked that the pubis and ischion equally concur to form the sym- 

 physU, so that this part of the pelvis is very large and divided crucially 

 by their suture. The oval holes are moderate and very nearly round. 

 The cotyloid fossa is not notched on the side of the oval hole ; but in 

 the Echidna its bottom is not ossified, and a great aperture is left in 

 that part of the skeleton. 



Skeleton of OrnithoryHchui : a, the supernumerary bones. 



Though the anterior part of the sternum and shoulder in the 

 Monotremes bears a resemblance to those of the Lizards, the rest of 

 that portion of the skeleton exhibits a conformation analogous to that 

 of '(iiadrupeds. The composition of the sternum is effected by succes- 

 sive pieces, and not by a cartilaginous dilatation as in the Saurians, 

 or a disc composed originally of five pieces, as in Birds. There are 

 four of these pieces, without reckoning either the Y-shaped bone or 

 the xiphoid cartilage, which in the Ornithorhynchus is ossified and 

 forms a fifth, making six in all. The piece which immediately follows 

 the Y-shaped bone is larger than the others, and in the Ornithorhynchm 

 exhibits traces of longitudinal division. The sternal portion of the 

 ribs is ossified as well an the other, as in Birds, and is joined to the 

 sternum by a cartilaginous portion, but there is no recurrent apophysis 

 to the dorsal ribs as in Birds. The sternal portion of the fifth ami 

 sixth ribs is very much dilated in the Echidna, and it is alao very 

 much dilated but not ossified in the first five or six false riba ; these 

 dilatations extend as far as the eighth in the Ornithorhynchus, and 

 become imbricated or laid over each other like tiles. In both genera 

 the last three false ribs have only very small inferior portions. In 



Echidna there are six true and nine false ribs on each side ; in Orni- 

 thorhynchus there are two more false ribs, but only two lumbar 

 vertebrae, whilst Echidna has three. Both genera have seven cervical 

 vertebne, like the rest of the Mammals. In Echidna they are flat 

 below, but have a sort of median crest in that direction in Ornitho- 

 rhynchus, and in the latter, even in the adult state, may be still 

 discerned the sutures which unite the transverse apophyses to the 

 body of the vertebra! ; here again is an analogy to the Reptiles. The 

 first four dorsal vertebrae in the latter genus have also small inferior 

 crests, which are wanting in Echidna; and in the caudal vertebrae a 

 still greater difference exists Echidna has only twelve, rapidly dimi- 

 nishing conically, whilat Ornithorhynchus has twenty at least, with 

 large and dilated transverse apophyses, forming a depressed tail, which 

 reminds the observer of that of the Beaver. The spinous processes 

 throughout have but little elevation, especially in Ornithorhynchus. 

 The vertebne, with the exception of those of the neck, do not retain 

 the sutures which join their parts longer than those of other 

 Mammals. 



In the Museum of the Royal College of Surgeons in London are 

 preparations displaying the internal structure of the Ornithorhynchus. 

 The cardiac and pyloric orifices of the stomach are closely approxi- 

 mated, as in the stomachs of birds. The greater part of the cavity 

 extends beyond these orifices, and increases as it descends into the 

 abdomen. The parietes are thin ; the two layers of muscular fibres 

 run in opposite directions, and are thickest along the curvature of the 

 pylorus. The intestines terminate in a common cloaca. 



The reproductive system is very characteristic of these animals. 

 In five apparently adult and full-grown Ornitkorhynchi examined by 

 Professor Owen, the mammary glands presented as many different 

 degrees of development. The number of lobes composing each gland 

 amounted from 150 to 200 ; they were elongated, sub-cylindrical, 

 disposed in an oblong flattened mass, and converged to a small oval 

 areola situated in the abdominal integument between 3 and 4 inches 

 anterior to the cloaca, and about an inch from the mesial line. The 

 lobes in the smaller glands preserved the same breadth to near the 

 points of insertion, but in the larger ones they were broadest at the 

 free extremity, measuring three or four lines across, and becoming 

 narrower to about one-third from the point of insertion, where they 

 ended in slender ducta. The lobes were almost all situated to the 

 outer side of the areola, and consequently converged towards the 

 mesial line of the body. The panniculus caruoms was interposed 

 between the glands and the integument, closely adhering to the latter, 

 but connected with the glands by loose cellular membrane. This 

 muscle was here nearly a line in thickness; its fibres were longitudinal, 

 and separating, left an elliptical space for the passage of the ducta of 

 the gland to the areola. 



Portion of the integument from the abdomen of Ornithorhynchus paradoius, 

 with the hairs removed so as to exhibit the mammary areola. (Owen, ' Philo- 

 sophical Transactions.') 



Magnified view of the mammary aieola, showing the orifices of the ducts o 

 the glandular lobule.*. (Owen, ' Philosophical Transactions.') 



