100 SHOULDER-GIRDLE AND BREAST-BONE. 



representative of the small specialised patch which breaks out near the sternal end of the clavicle 

 in the Mammals. The semi-osseous epicoracoid, lying more in front of than below the coracoid, 

 is seen to be the true morphological counterpart of the epicoracoid of the Monotreme, in which 

 this part has an ectosteal sheath, as well as the coracoid ; and in which the coracoid shaft reaches 

 to the base of the cartilage postero-inferiorly. 



Anguis D. This was an old individual, and serves to show how little relative change takes 

 place from the time when the Snake is only three inches long to its last condition. Fig. 6 shows 

 the outside of the Shoulder-plates, magnified twelve diameters ; and by comparing this figure 

 with that of Anguis A (fig. 2), it will be seen that the changes have been principally those of bulk, 

 and not of relative modification. The base of the supra-scapula (s. sc.) is affected by the three 

 scapular bony rays, but the rest is quite soft. The scapula itself (sc.) is surrounded by clear 

 cartilage ; most of the prae-coracoid (p. cr.) is unossified, and so also is the outer half of the 

 epicoracoid (e. cr.). The base of the coracoid (cr.) is extended, and the fenestra (cr. f.) is rela- 

 tively less ; the epicoracoid flaps overlap nearly as much as in Anguis A, the right overlying 

 the left. The clavicles (cl.) have become two or three times as stout, relatively ; but their shape is 

 very little altered. The interclavicle (i. cl.) has become a single, nail-shaped bone, with a fissure 

 through it, and a notch below its head, also showing where it was once quite divided into two 

 pieces. It is now a good generalised representative of the so-called " ento-sternum" of the 

 Chelonian, and " epi-sternum" of the Lizard and the Monotreme. From its position below and 

 in front of the Sternum it stops up the chink in the latter, and appears on the inside behind the 

 bridge of cartilage, which has cemented together the " inner coracoid lips" of the true Sternum 

 (Plate VIII, fig. 7, i. cl., cr. g.). The Sternum (figs. 6 and 7, st.) has a greater antero-posterior 

 diameter than in the young specimen, and there is nearly room for a first thoracoid rib behind 

 the coracoids. The primordial division appears as a lunate notch in front and behind, and as 

 a chink behind the confluent coracoid lips (fig. 7, st. f.) ; here we see the inter-clavicle fixed like 

 a wedge in a board. The "outer coracoid lips" are more extensive than the inner (fig. 7, cr. g.), 

 but they are both well defined ; the bony patches have met and coalesced at the mid-line, and 

 they keep very clear of the metosteal "inter-clavicle," showing their independence of and want 

 of morphological relation to it. 



3. " SAURIA SQUAMATA TYPICA." 

 A. With three Shoulder-splints, viz. a pair of Clavicles and an " Inter -clavicle." 



\ 



I shall now undertake the description of the Shoulder-girdle and Sternum in the Lacertilia 

 generally ; excluding, at present, the Chamseleonidse, because of the absence in them of the usual 

 Shoulder-splints. The field, however, is so very extensive, that I cannot find either time or space 

 for half the material at my disposal, and I must choose certain important examples which may do 

 duty for the numberless Lacertian types. I shall very much enrich my paper by giving Rathke's 

 account of the Breast-bone and its inter-clavicular splint (supposed by him to be the anterior 

 sternal bone) in many species not worked out by me. The following translation (by Mr. Power) 



