STRANDED AT LONGNIDDRY. 229 



muscular wall at the bottom of some of the pouches was often so thin as to be 

 translucent when held up to the light. Many of these pouches were situated 

 parallel and close to the auriculo-ventricular groove. 



The left ventricle had thicker walls than the right, and, in connection with 

 its walls and auricular opening, carnese columnar, musculi papillares, chordae 

 tendinese, and a bicuspid valve were seen. 



The arch of the aorta in the mother rivalled in its calibre one of the main 

 pipes for the supply of water to a district of a large city. The internal circum- 

 ference of its ascending part was 3 feet 2 inches, whilst its coat varied in thick- 

 ness from 1^ to 1^ inch. The coat was distinctly laminated, of a yellow colour, 

 and very elastic. A well-defined inner membrane lined it and the other parts of 

 the arterial and venous systems. The external circumference of the aorta in 

 the foetus was 10 inches. It then dilated prior to giving origin to the great 

 branches of the arch, and immediately beyond these vessels it diminished 

 materially in size as it became the posterior thoracic aorta. The external cir- 

 cumference of the innominate artery in the mother was 1 foot 9 inches. 



The aorta arched to the left over the root of the lung (Plate VII. fig. 28). 

 A pair of coronary arteries (a) arose from the commencement of its ascending 

 part, one passing on each side of the root of the pulmonary artery. Each 

 coronary immediately subdivided into three branches, the largest of which 

 turned round its own margin of the heart in the auriculo-ventricular groove, and 

 supplied the corresponding auricle and ventricle. The second branch of the 

 right coronary entered the wall of the right auricle ; the third turned round the 

 root of the pulmonary artery. The second branch of the left coronary artery 

 descended in the anterior inter- ventricular groove ; the third passed to the 

 substance of the left ventricle. In the mother each coronary artery was as 

 large as the posterior aorta of an ox. 



From the anterior surface of the transverse part of the arch three large 

 branches arose, the brachio-cephalic, left carotid, and left subclavian (b, c, d). 

 The right branch, by far the largest, was the arteria innominata or brachio- 

 cephalic (a). Five inches (in the foetus) from its origin it bifurcated into a right 

 common carotid (e) and right subclavian (/). The right subclavian gave off, 

 one inch from its origin, a large branch, the right posterior thoracic [g), which 

 was traced into the great thoracic rete mirabile. One inch and a-half further 

 on the subclavian bifurcated into the axillary (h) and internal mammary (i) 

 arteries, the latter of which was somewhat the larger of the two, and supplied 

 the inferior wall of the chest. The axillary passed in front of the first rib, 

 immediately above the scalenus anticus muscle ; but before doing so it gave off 

 a considerable branch which ran forwards along the side of the neck. The 

 axillary was traced into the flipper, and, in the dissection of the fore-arm, 



VOL. XXVI. PART I. 3 O 



