442 ORGANS OF SENSE. 



iform interlacement, which constitutes the lumbar aortic plexus ; the lowei 

 branches cross the common iliac arteries, and unite over the promontory 

 of the sacrum, to form the hypogastric plexus. 



The Lumbar aortic plexus is formed by branches from the lumbar gan- 

 glia, and receives filaments from the solar and superior mesenteric plex- 

 uses. It sends filaments to the inferior mesenteric plexus, and terminates 

 in the hypogastric plexus. 



The Hypogastric plexus is formed by the termination of the aortic 

 plexus, and by the union of branches from the lower lumbar ganglia. It 

 is situated over the promontory of the sacrum, between the two common 

 iliac arteries, and bifurcates inferiorly into two lateral portions, which 

 communicate with branches from the fourth and fifth sacral nerves. It 

 distributes branches to all the viscera of the pelvis, and sends filaments 

 which accompany the branches of the internal iliac artery. 



SACRAL GAN GL IA. 



The Saw &i ganglia are four or five in number on each side. They are 

 situated upon the sacrum, close to the anterior sacral foramina, and re- 

 semble the lumbar ganglia in form and mode of connexion, although much 

 smaller in size. 



The superior and inferior branches communicate with the ganglia above 

 arid below. 



The external branches communicate with the sacral nerves. 



The internal branches communicate very freely with the lateral divisions 

 of the hypogastric plexus, and are distributed to the pelvic viscera. The 

 last pair of sacral ganglia give off branches which join a small ganglion, 

 situated on the first bone of the coccyx, called the ganglion impar, or 

 azygos. This ganglion resembles in its position and function the ganglion 

 of Ribes, serving to connect the inferior extremity of the sympathetic sys- 

 tem, as does the former ganglion its upper extremity. It gives off a few 

 small branches to the coccyx and rectum. 



CHAPTER X. 



ORGANS OF SENSE. 



THE organs of sense, the instruments by which the animal frame is 

 brought into relation with surrounding nature, are five in number. Four 

 of these organs are situated within the head : viz. the apparatus of smell, 

 sight, hearing, and taste ; and the remaining organ, of touch, is resident 

 in the skin, and distributed over the surface of the body. 



THE NOSE AND NASAL 



The organ of smell consists essentially of two parts: one external, tJie 

 nose ; the other internal, the nasal fossae. 



The nose is the triangular pyramid which projects from the centre of 

 the face, immediately above the upper lip. Superiorly it is connected 



