OCR Text |
Show 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 limbs, which calls for strength in the median line. Fig. VI. m 1. Bibs in the position of inspiration. 2. Bibs 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 corresponds with the condition in the Ostrich of 15 days' incubation. 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. B, resultant 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 m y 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 ' H E R M I N I E R . Recherches sur la Marche de l'ossification dans le Sternum des Oiseaux, pour faire suite aux travaux de |