DIAPHRAGM. 



organ which could exert no influence on the 

 external form ; nor was it to be expected in a 

 muscle which is not wholly voluntary. In this 

 article it is intended to describe, 1st, the form, 

 structure, and organization of the diaphragm ; 

 2nd, its uses ; and, 3rd, its malformations and 

 diseases. 



Fig. 1. 



AlxJominal surface of the diaphragm, 



Fig. 2. 



Tlioracic turf ace teat from before. 

 Fig. 3. 



surface seen fmm behind, the verlebrec being 

 removed. 



For the convenience of description the dia- 

 phragm is usually divided into two portions 

 the upper, which is called the costal, or true or 

 greater muscle ; and the lower, which is named 

 the vertebral, or smaller, and is also well known 

 as the crura or pillars. This division is sanc- 

 tioned by the situation, the shape, and the use3 

 of the two portions. 



The upper portion, placed tranversely, (sep- 

 tum transversum,) is thin, but of great super- 

 ficial extent, being connected by its margins to 

 the entire circumference of the inferior outlet of 

 the thorax. Narrow between the sternum and 

 spine, it spreads out on each side into large 

 wings, and its outline bears some resemblance 

 to the figure of eight laid on the side, thus W . 

 The centre is tendinous ; the border consists of 

 fleshy fibres. The tendinous part (fig. \, T) 

 (centrum tendincum, s. nerveum, s. phrenicum, 

 cordif'orm tendon) is of considerable size, and 

 in shape resembles the trefoil leaf. It presents 

 a large semicircular notch behind towards the 

 spine, and is deeply divided on its anterior 

 margin into three lobes, of which one points for- 

 wards and one to each side. Of these lobes the 

 right is usually the largest, the left the smallest; 

 the anterior is the shortest, and sometimes the 

 broadest; the left is the narrowest and often 

 the longest. But these proportions will be 

 found to vary in different individuals. The 

 tendon is composed of fibres which pursue 

 various courses. The greater number radiate 

 from the vertebral notch ; these are crossed by 

 others which run in every direction, and which 

 seem to be continuous with the muscular 

 fibres ; and others again appear to be laid on 

 the tendon as accessaries, rather than as con- 

 tributing to its texture. These last are most 

 distinctly seen in old men, and on the under 

 surface of the right lobe. The tendinous centre 

 forms nearly the highest part of the arch. It is 

 less curved than the fleshy portion, and more 

 fixed in its position. One large opening pre- 

 sents itself here, between the right and middle 

 lobes, through which the vena cava passes to 

 the heart. 



From the anterior and lateral margins of this 

 tendon the muscular fibres pass off in arches, 

 to be inserted into all the base of the thorax by 

 digitations which mix with those of the trans- 

 versus abdominis. 



Beginning in front, we find two slender fasci- 

 culi running downwards and forwards to the 

 ensiform cartilage. These are separated from 

 each other by a line of cellular tissue, marking 

 the median line of the muscle; sometimes one 

 or both of these bundles may be absent, pro- 

 bably resulting from an arrest of formation. 

 To the outside of these, on each side, a con- 

 siderable triangular interval exists, where the 

 pleura and peritoneum are separated only by 

 cellular substance. Here some small branches 

 of the internal mammary artery pass to the ab- 

 domen ; and in this situation fluids might easily 

 find their way from the cellular tissue of one 

 cavity to that of the other. The fibres next in 

 order, bounding these spaces externally-, are 

 much longer ; they pass outwards and down- 

 wards to the seventh rib, and are inserted by a 



