376 



MONOTREMATA. 



transverse processes, and the first eleven have 

 also spinous and articular processes. The 

 transverse processes are broad and depressed ; 

 they gradually increase in length to the tenth 

 caudal, then as gradually diminish to the twen- 

 tieth; their extremities are expanded, and, 

 from the fifth backwards, are thickened and 

 tuberculate. The spinous processes progres- 

 sively diminish in height from the first 

 caudal. The first six caudal vertebrae have 

 both posterior and anterior oblique processes, 

 and are joined together both by these and by 

 the articular surfaces of the body : the anterior 

 articular processes are present, but progres- 

 sively diminish in size from the seventh to the 

 sixteenth vertebrae, and are not subservient to 

 their reciprocal articulation. Inferior spinous 

 processes are developed from the bodies of 

 the third to the nineteenth caudal vertebra 

 inclusive ; but there are no haemapophyses 

 articulated to the vertebral interspaces, as in 

 many Marsupials and the Edentata. In the 

 Echidna the inferior spinous processes are 

 absent ; but rudiments of haemapophyses are 

 connected with the interspaces of one or two 

 of the middle vertebras of the tail. The cau- 

 dal vertebras in the Ornithorhynchus are of 

 nearly the same length to the two last; they 

 progressively diminish in vertical diameter as 

 they recede from the trunk, and are chiefly 

 remarkable for their breadth and flatness ; 

 resembling in this respect, as Cuvier has ob- 

 served, the caudal vertebra; of the Beaver, and 

 we might add those of the Cetacea; the hori- 

 zor.tally extended tail having a similar relation 

 to the frequent need which an aquatic animal 

 with hot blood and a quick respiration of air 

 has to ascend rapidly to the surface of the 

 water. 



Of the pectoral extremities. Cuvier* justly 

 observes that the most remarkable part of tiie 

 osteology of the Monotremes is the organiza- 

 tion of the shoulder; which corresponds with 

 that of birds, and still more witli that of 

 lizards. 



Had these anomalous Mammals been ex- 

 tinct, and their fossilized skeleton alone, as in 

 the Ichthyosauri, been preserved for the con- 

 templation of the naturalist, the perplexity 

 which the combination of this structure with 

 the mammalian conditions of the skull and 

 vertebrae would have occasioned maybe readily 

 conceived. 



The scapula (/) is represented detached, with 

 the coracoid (o), at G, fig. 173; /* is the 

 cartilage appended to the short convex base. 

 The scapula is long, narrower than in most 

 Mammalia, and has its posterior vertebral 

 angle so much produced, as to give it a re- 

 semblance to the scapula of the bird and 

 saurian : this resemblance is farther increased 

 by the origin of the spine close to the anterior 

 costa, and by the spine being bent forwards 

 so as to seem to form a continuation of the 

 external surface of the scapula, which is thus 

 rendered concave in the Urnilhorhynclius. 



* Ossem. Foss. v. pt. 1, p. 146. 



The spine, however, terminates in a freely pro- 

 jecting acromion. 



The true anterior costa is, in this Monotreme, 

 represented by a ridge which traverses ob- 

 liquely the inner and convex side of the sca- 

 pula, from the anterior vertebral angle to the 

 neck of the bone. In the Echidna this ridge 

 is nearly obsolete, and the spine of the sca- 

 pula is bent so as to form a more direct con- 

 tinuation of body of the scapula with the plane 

 of which it is nearly parallel : the acromial ter- 

 mination is slightly twisted. 



Both Cuvier and Meckel describe the spi- 

 nous process of the scapula as the anterior 

 margin, (superior costa in human anatomy,) 

 and consequently consider the spine of the 

 scapula as being absent. Cuvier says, " Le 

 bord anterieure descend presque droit jusqu'a 

 1'endroit ou il se courbe en dedans pour former 

 une apophyse, qui porte la fourchette." Meckel 

 recognises this process as the acromion : " Margo 

 anterior partis superioris versus inferiora ex- 

 trorsum primo flexus, dein eminentiam, acro- 

 mion, antrorsum et introrsum versam, emittit." 

 The ' margo anterior' of Meckel, ' bord ante- 

 rieure' of Cuvier, is, in fact, the true spine of 

 the scapula, and the true ' margo anterior' is 

 the ridge above described. The proof of this 

 is afforded by the origin of the supra-spinatus 

 muscle which occupies the space between 

 Meckel's ' margo anterior' and the ridge 

 which I regard as the true anterior costa, and 

 which is not noticed by either of the anato- 

 mists above quoted. 



Since the scapula is peculiarly characterized 

 in Mammalia by the presence of a spine and 

 in Ovipara by its absence, its recognition in 

 the Monotremes, under the modification by 

 which its apparent absence is occasioned, and 

 the transition to the oviparous type of this bone 

 is effected, becomes a subject of especial in- 

 terest. 



The whole scapula is broader, thicker, and 

 less curved in the Echidna than in the Orni- 

 thorhynchus. In both Monotremes, the pos- 

 terior margin or costa is concave, most so in 

 the Ornithorhyncltm, and in both it is turned 

 towards the trunk, so that the sub-scapular 

 surface looks obliquely forwards and inwards. 

 The articular surface is divided into two facets: 

 the one, internal and flat, articulates with the 

 coracoid; the other, external, is slightly con- 

 cave, and contributes, with a similar but nar- 

 rower concave surface of the coracoid, to form 

 the glenoid cavity for the humerus. 



The coracoid (Jig- 173, G, o) early coalesces 

 with the scapula in the Ornithorhynchus ; it main- 

 tains its independent condition to a later period 

 in the Echidna. In both it is a strong, subcom- 

 pressed, subelonsate bone, expanded at both 

 ends; one of these is articulated and anchylosed 

 with the scapula, as above described ; the other 

 is joined to the anterior and external facet of the 

 manubrium sterni. The posterior margin of 

 the coracoid is concave and free ; the anterior 

 margin is straight and articulated with a thin 

 broad irregularly quadrilateral plate of bone in 

 the Ornithorhynchus, and a thicker and nar- 



