REPRODUCTIVE SYSTEM GENERALLY. 255 



blood is suffered to proceed, as in the adult, into the right 

 ventricle, and thence into the pulmonary artery ; where 

 occurs another structural impediment to the passage of the 

 foetal blood. The pulmonary artery communicates with 

 the posterior aorta, by means of a lateral branch, which 

 looks, as it were, a continuation of the arterial trunk. This 

 branch of free communication takes the greater portion of 

 the blood, sent by the right ventricle up the pulmonic 

 artery, into the posterior aorta. The small portion of blood 

 which passes through the collapsed lungs is returned by the 

 pulmonic veins into the left auricle ; where, uniting wdth 

 that which had escaped through the foramen ovale, both 

 enter the left ventricle, and pass into the aorta ; the major 

 part being sent up the anterior aorta, and the rest in the 

 posterior aorta, uniting with that received by the ductus 

 arteriosus, the whole becomes distributed over the body in 

 the usual manner. The umbiHcal arteries (Fig 14 . /c) of the 

 foetal colt are very considerable vessels, derived from the 

 internal ihacs, immediately after their origin : in their pas- 

 sage, each towards its appropriate side of the bladder, they 

 approximate and join the urachus, proceeding togetlier 

 as a part of the umbilical cord. The umbilical vein, after 

 birth, dries up, and is converted into a ligament of the 

 liver. 



Descent of the testicles. — It is necessary, before we describe 

 this interesting process in the foetal economy, that we say 

 something of the construction of the track by which these 

 organs reach the scrotum. The abdominal rings, for there 

 are an outer and an inner, as there are two ends to the 

 straight and limited inguinal canal, are situated within the 

 fleshy walls of the abdomen. The walls of the abdomen 

 are mainly formed of four pairs of large muscles, whose 

 central line of union forms the linea alba, which is seen 

 about its middle, perforated by the umbilicus or navel. 

 The obliquus externus is the most external of these, and 

 arises from the anterior spine of the ilium, and from the 

 fascia lumborura, to be inserted into the posterior border 

 of the fourteenth hindermost ribs. It is externally covered 

 by a yellow elastic ligament of some substance, and in- 

 feriorly meets its fellow at the linea alba. From its inser- 

 tion (see Plate II. 1 1) its fibres are directed obliquely down- 



