28 Descriptions of Preparations. 



depends mainly upon the opening- and closing of the angles formed 

 by the sternal ribs with the vertebral ribs and with the sternum. 

 In the Fowl the fontanelle in the posterior part of the Pigeon^s 

 breastbone is represented by a deep emargination^ reaching from 

 the level of the xiphisternal portion of the sternum up nearly, or 

 quite in some specimens, to that of the last or fourth articular 

 facet for the fourth sternal rib. The hyposternal element of the 

 sternum is thus divided into two long distally pedate processes, 

 which, it may be remarked, are developed on each side from a 

 single centre of ossification, distinct and apart from the three 

 others from which the sternum is made up in Rasores. The hyo- 

 sternal processes are continued forward in the direction of the 

 articular costal border, instead of taking a direction at i*ight angles 

 to it as in the Pigeon. The coracoid grooves are continued into 

 each other b}^ means of a canal which pierces the base of a vertical 

 lamella prolonged downwards from the episternum into the ento- 

 sternal raphe. The ei)isternum differs also from that of the Pigeon 

 in having no pneumatic foramina anteriorly at its base, though it 

 is sometimes perforated here by a canal oj^ening on the upper or 

 visceral surface of the bone. Pneumatic foramina, it may be 

 added, are in the sternum of the Fowl, as in many or most other 

 parts of its osseous system, much more sparingly distributed than 

 in the Pigeon, as may be noted in the intervals of the costal artic- 

 ular facets, and superiorly, along the middle line, and internally to 

 the costal processes on either side. The entosternal crista, which, 

 owing possibly to unequal pressure during incubation, is rarely 

 straight from before backwards, slopes up to its maximum height at 

 a point posterior to the level of the last costal facet, instead of rising 

 to it almost immediately from the episternal level as in the Pigeon. 

 It is much less deep relatively, and the space marked out upon it for 

 the great pectoral muscle is very little deeper absolutely than the 

 corresponding parts in the Pigeon. The xiphisternal portion of the 

 sternum is a little wider and more concave upwards than the ento- 

 sternum, and by virtue of its shape furnishes some protection to the 

 gizzard and other viscera it is in relation with during incubation. 



The FowPs pelvis differs from that of the Pigeon in general 

 shape and texture much as its cranium does from that of the same 

 bird, being, as it is, more elongate and angular and less polished. As 

 minor points of difference, which are nevertheless with certain ex- 



