124 SHOULDER-GIRDLE AND BREAST-BONE. 



these creatures as to their Sternum, as I find one and an odd one to the anterior piece, and two 

 to the posterior in C. vulgaris, and in C. pumilus one and three. Moreover, morphologically, his 

 specimen could not have been further advanced than the Cyclodonts (see Plate X), where the 

 double sternal horns have partly united together at the mid-line ; and by segmentation have 

 nearly made, from those horns, two additional sternal regions. 



Example 2. Chamceleo pumilus, Gmelin. 



My specimen of Chamceleo pumilus is further advanced than any described by 

 Rathke, but it has enabled me to reconcile his descriptions with my observations. I find no 

 connection of a cervical rib with the Sternum ; and there is, therefore, only one pair united 

 with the prse-sternum, which is shaped like that of C. vulgaris. The two halves of the meso- 

 sternum are well united, and the whole Sternum is well ossified for a Lizard. The first and 

 second thoracic sternal ribs are rather near each other ; then there is a long "internode;" and then 

 two pairs very near each other, as in Cyclodus (Plate X) ; between the last pair of sternal ribs the 

 Sternum is emarginate, and these ribs are imperfectly segmented from it, exactly as in the Cyclodonts. 

 Behind the fourth thoracic rib-girdle comes an arch with a small raetasternal, and then the ribs 

 merely meet, and unite by suture. Now, it appears to me that my specimen of C. vulgaris, when 

 in an early stage, had its fourth pair of thoracic ribs entirely detached from the short xiphi- 

 sternal horns ; that these severed ribs, whilst the creature grew in length, became more and 

 more removed from the third pair, and that they then met, coalesced, and, growing pcdate, 

 formed the " metasternal plate." Meanwhile, the short xiphisternal horns, being free, grew not 

 only towards each other and coalesced, but also grew backwards, so as to form a free, single 

 xiphisternum, exactly like that of an ordinary Mammal. 



That there is no real difference between these two Classes in the formation of the 

 xiphi-sternum I feel certain, for the condition of the Sternum here described in Chameeleo 

 pumilus, and also in the Cyclodonts, is precisely what I must describe, in the sequel, in the 

 Delphinoid Cetacea. 



I will now give some very important remarks of Rathke upon the number of ribs connected 

 with the Sternum, and then compare his observations with my own. 



RATHKE, 'Brustbein der Saurier,' pp. 18, 19. 



XIV. In the typical Scaly Lizards several ribs are always in relation with the Sternum; still, in relation 

 to their own number only one or two are in intimate connection with it. In these the Sternum usually 

 consists of an anterior [inter-clavicle] and a posterior segment [true Sternuni] ; and then when this is the 

 case it is always the latter which is connected to several of the ribs. But of this segment, again, it 

 may be either only the anterior division, and thus the most extensive part of the whole Sternum, which 

 is connected with the ribs, or it may be exclusively the posterior division, which usually forms a 



