Knott — On Muscular Anomalies. 627 



L XXX VI. — McscuLiE ■ Anomalies, including those of the 



DlATHKA&M, AND SfBDIAPEKAGMATIC ReGIONS OF THE IIuMAN BoDT. 



By J. F. Knott, F. E. C. S. I. 



[Eead, June 26, 1882.] 



In a Paper read before the Royal Irish Academy last year (vide these 

 Proceedings, ante, page 407) I gave a short description of the leading 

 Abnormalities in Human Myology which had come under my notice dur- 

 ing a dissecting-room experience of four winters. This was fairly com- 

 plete, so far as the muscles of the head, neck, and upper extremities 

 are concerned, but included only a few of those of the trunk and 

 lower limbs. Some of my scattered notes were mislaid at that time, 

 and I was obliged to postpone their publication. Accordingly, I take 

 the present opportunity of laying before the Academy the results of 

 my observations on the muscular variations occurring in the infra-dia- 

 phragmatic segment of the human body, during an anatomical experience 

 of five winter sessions. 



Diaphragm {phren, septum transversum, midriff). — This muscle I 

 have examined, with a special view to the detection of anomalies, in 

 thirty-six cases. Besides the variations observed in these more special 

 instances, I made notes, from time to time, of peculiarities which 

 were casually observed, or to which my attention was called by the 

 dissector. Special care was given to the examination of the aortic 

 opening in the cases tabulated. 



Crura. {Appendices of Haller, Capita of Albinus, Processus of 

 Santorini). — The cms of either side is divided by Professor "W". Krause 

 into three parts : crus internum (s. mediate), crus medium, and crus ex- 

 ternum. Of these, the fi.rst is attached to the bodies of the third and 

 fourth vertebrae, and the intervertebral disc between ; the middle crus 

 arises by a small and pointed process from the front of the second 

 vertebra, while the lateral crus, shorter and broader, arises from the 

 anterior and outer aspects of the body and front of the transverse process 

 of the first lumbar vertebra. Through the interval between the crus 

 internum and crus medium pass the splanchnic nerves ; lying on the 

 outer side of which is, on the right side, the major azygos vein; on the 

 left side, the minor. Between the middle and external crura passes 

 the sympathetic chain on either side. The tendinous margin of the 

 external crus forms the ligamentum arcuatum internum. 



This I regard as much the best description of the arrangement and 

 attachments of the crura. Variations in the course of the veins and 

 nerves are, hoAvever, often met with. The hiatus aorticus not un- 

 frequently transmits the n. splanchnicus major ; sometimes both this 

 nerve and the azygos vein (major or minor). The minor splanchnic 

 sometimes passes through a slit in the crus internum, thus subdivid- 



R. I. A, PKOC, SEK. II. VOL. III. — SCIENCE. 3 K 



