110 SHOULDER GIRDLE AND BREAST-BONE. 



if perfect, would have made two more meso-sternal regions with the two pairs of ribs articulated 

 to these parts as their own proper key-bones : instances yet to be given will explain this. Fig. 5 

 shows one of these bars in section, magnified twelve diameters, with its perichondrium, hyaline 

 cartilage, and endosteal ring, enclosing, here and there, islets of cartilage. Before the sternal 

 ribs reach the fully ossified vertebral ribs, a great constriction is observed ; this arises from 

 the partial segmentation of what I propose to call the " intermediate rib :" it is better seen in 

 some other types to be hereafter described. 



The first thoracic rib belongs to the seventh vertebra ; the last cervical rib is free, and is ten 

 lines long ; the penultimate is six lines in length, but the other four cervical vertebrae have no 

 distinct ribs. 1 



Example 2. Lamanctus longipes, Wiegmann. 



This very beautiful Mexican Lizard has a simpler Shoulder-girdle than the Iguana ; this will 

 be seen by comparing the figures in Plate IX : those of Lcenianctus (figs. 7 9) are magnified three 

 diameters, so as to appear equal to their counterparts in the Iguana. 



The supra-scapula (fig. 7, s. sc.) is more symmetrically fan-shaped than in the Iguana, and it 

 has at least seven lobes to its endosteal layer: this gives it the appearance of a Cock's comb. 

 The high scapula (sc.) is almost entirely covered by ectosteal bone ; there is, however, a small 

 epiphysis on the front of the meso-scapula : this is hidden, in the figure, by the clavicle (cl.). 

 There is a shallow scapular notch (sc. n.) dividing the main part from the meso-scapula (m. sc.); 

 but this was much deeper originally, before the growth of the periosteal layers of bone, indicated 

 in the figure by a shaded groove. The coraco-scapular fenestra of the Iguana is here represented 

 by a notch (c. s. n.); this is large and deep, and depends upon the complete fission of the plate 

 anteriorly, as in the upper notch. The coracoid (cr.) is a broad ray, convex on the outside, and 

 very much scooped within, where the meso-coracoid margin is seen to be much thickened, but to 

 be not otherwise differentiated. A suture can be seen in front of the glenoid cup (gl.), and below 

 it a nerve-passage, which is double on the right side (fig. 8) : in front of this canal is the large 

 elliptical, down-turned coracoid fenestra, the space so familiar to us in the Batrachia. The lesser 

 fork of the coracoid ossifies more than half of the prae- coracoid bar (p. cr.), which has no 

 differentiation from the epicoracoid (e. cr.) save the acute angle at which it becomes con- 

 tinuous with that semi-osseous headland of the coracoid : the right and left flaps overlap each other 

 to some extent. 



The antero-lateral margins of the Sternum (st.) are only three fifths the length of the 

 postero-lateral, and not equal, as in the Iguana; the former are thickened considerably both below 

 (fig. 8) and above (fig. 9) ; this latter figure shows that the lower lips (1. c. 1.) project further 

 forwards than the upper (u. c. 1.), which unite at a rather obtuse angle, and have within that 

 angle two swollen hillocks of cartilage, which abruptly bound the great sternal fontanelle ante- 

 riorly. This thickening, and the gap behind it, will often turn up again in the Bird-class ; here 

 the primordial cleft is seen to be occupied by the hinder part of the " inter-clavicle" (i. cl.), which 



1 In Plate IX, fig. 1, the Shoulder-plate is shown leaning forwards from the first rib, further than 

 what is found in nature ; this has been done for the sake of displaying the parts ; the great plate itself 

 stands too erect in the figure, but it was necessary to give the actual and relative size of the bars 

 and fenestrse. 



