80 SHOULDER-GIRDLE AND BREAST-BONE. 



periosteum, which is only inflected because the sheath of bone has enlarged the Shoulder-plate 

 by its own thickness. 1 



Stage 2, Sana S. In a few days the tail becomes reduced to half its former length and 

 bulk ; and by this time the moieties of the Shoulder-girdle have grown considerably, but not so 

 much as the intestines have decreased in size, for they are as completely metamorphosed in the 

 course of time as those of a Caterpillar when it takes on its transformations ; whilst in the 

 Tadpole the coil is extremely long, there is only a single loop in an otherwise straight bowel by 

 the time the curtailment of the young Frog is complete. In this next stage (Rana S.) the tail 

 is scarcely more than half its former length, and the reduction of the contents of the chest and 

 growth of the cartilages have brought them not only together, but to overlap in the usual way. 

 Plate V, fig. 3 shows a small part of the overlapping coracoids at this stage, magnified seventy- 

 five diameters, and seen from within ; and it is seen that their edges are flanked by a new growth 

 of soft and delicate cartilage, which is in immediate contact with the serous membrane lining the 

 common thoracico-abdominal cavity : this is the first appreciable appearance of the moieties of 

 the true or costal Sternum, which is developed at a great distance from the arrested vertebral 

 ribs, but which crops out in the basal region in correlation to the Shoulder-girdle, for which it 

 seems to have a sort of organic affinity. It may help comparison to remark that this first tract 

 of cartilage, which lies directly behind, within, and mesiad of the epicoracoid angles, corresponds 

 to the anterior half of the human " manubrium sterni," which is, in reality, the keystone, in us, of 

 the seventh cervical vertebra. The side-walls of this seventh somatome, and also of the six 

 preceding somatomes, are deficient in cartilage ; the ribs, in the cartilaginous stage, never being 

 segmented off from their centrums, as they are in the thoracic region. And this is one reason 

 why the Shoulder-girdle has been confounded with the costal girdles ; for, lying in front of these 

 latter hoops, and being the only cartilaginous bars interposed between the skin and the space 

 containing the oesophagus and trachea, they have been supposed to lie in the same plane as the 

 ribs. Wherever the limb-plates are coincident, vertically, with the costal arches, they and their 

 muscles always overlap, or lie in an outer transverse plane. If the diagram (Plate V, fig. 2) be 

 looked at, it wiU be seen that, at least, the three anterior vertebras of the Tadpole are cervical ; 

 the same may be said of the ordinary Osseous Pish. I shall, throughout this paper, consider the 

 first perfect costal arch, as homologous with our first, and the last vertebra that has ribs that are 

 imperfect whether on one or on both sides I shall put down as agreeing with the last cervical 

 in human anatomy. 



Using as much as possible the old, somewhat arbitrary, but most convenient region-terms, I 

 shall nevertheless, stand reverently aside, whilst Nature makes more or fewer vertebrae in any 

 particular region ; and, as her collocations are all so thoroughly comfortable as well as conformable, 

 I am riot fain to suppose that she has been under the necessity of shifting, replacing, and misplacing 

 her bars, her rays, and her plates ; as though a necessity had been laid upon her, and that she 

 must, perforce, make all things according to the pattern showed to her, at any cost. 



1 At present, the prse-coracoid bar is larger than the coracoid, as in Systoma gibbosum, and in 

 the pelvis of the Turtle ; and the " omosternum" and true sternum have not yet made their appear- 

 ance ; and, moreover, this early Shoulder-plate is extremely unlike that of the Newi at a similar stage. 

 (See Plate III, fig. 7.) 



