1885.] 



MISS B. LINDSAY ON THE AVIAN STERNUM. 



713 



Further, the union of the two halves of the sternum is rendered 

 imperative by the strain involved in the moving of the fore hmbs, 

 which calls for strength in the median line. 



Fig. VI. 



1. Ribs in the position of inspiration. 



2. Eibs at the end of expiration, packed into loops. 



3. The primitive costal band ; m, median line. 



4. Theoretical diagram of the posterior border of the sternum, as influenced by 



no muscle but the rectus; r.l., r.m., strain of the rectus medianus and 

 rectus lateralis, producing lateral and median processes. This corre- 

 sponds with the condition in the Ostrich of 15 days' ineubatioH. 



5. Lateral process modified by the lateral strain of o.e , the obliquus externus, 



passing from the sternum to the side of the abdominal region. E, re- 

 sultant of its strain and that of the rectus lateralis, acting at the outer 

 point of the process. This diagram corresponds with the older Ostrich 

 embryos. 

 In the Ostrich, owing to the extreme smallness of the pectoral muscles, the 



mechanical relations of the posterior border of the sternum are simple compared 



with those existing in other birds. 



The researches described in the above paper were undertaken at 

 the instance of Dr. Gadow, whom I have to thank, not only for 

 constant help and criticism throughout my work, but also for nearly 

 the whole of the material used. I must likewise record my thanks 

 to Mr. Sedgwick for the use of sections of the Chick belonging to 

 the Morphological Laboratory, Cambridge ; and to Miss Clarke 

 (lately Demonstrator of Biology at Newnham College, Cambridge) for 

 part of the material used and for kindness in literary help. 



Literature. 



1. L'Herminier. Recherches sur la Marche de rossification 

 dans le Sternum des Oiseaus, pour faire suite aux travaux de 



