PLATE LVII. 



THE FRONT OF THE NECK AND THORAX OF A 

 NEARLY FULL -TERM FOETUS. 



In this plate the anterior view of a nearly full-term fetus is shown. The front 

 of the thorax was removed to show the relations of the thymus gland, and the position 

 of the lungs when not expanded. 



The ligament of the thymus gland, which was described by the late Mr. Arthur 

 1 1 '-lignum in Morris's ' Anatomy,' is only present on one side, but it shows in its centre 

 a slight bulging which encloses a small isolated mass of gland structure, such as is often 

 found in it. Very often the ligament is present on both sides, the thymus gland 

 being thus tied up to the lower border of the thyroid gland. The thymus is developed 

 in the foetus as a bilateral tubular prolongation of the third visceral cleft, which grows 

 ilown along the side and front of the trachea to join the fellow of the opposite side and 

 so form a median organ. It also receives, a portion of the epithelium from the fourth 

 visceral cleft. 



The thyroid gland is developed from two sources, the lateral lobes as diverticula 

 from the fourth visceral clefts, while the median lobe or isthmus is a median diverticulum 

 from the pharyngeal hypohlast opposite the second visceral arch, which grows down the 

 front of the trachea and unites with the lateral lobes. This remains in the fcetus for 

 some time as the thyreoglossal duct, opening on the surface of the tongue in the 

 foramen crccum. If, as occasionally happens, the upper part remains pervious, it is 

 called the lingual duct. In the lower part the pyramidal middle portion or isthmus of 

 the gland is developed, which is usually attached by a fibrous cord to the thyroid 

 cartilage or thyro-hyoid ligament, and is called the ligament of the thyroid gland. 



This plate shows the relatively small space occupied by the lungs in the foetal chest 

 before inflation. In this condition they are of a uniform, firm texture throughout, and 

 iubJo in colour and structure the adult liver; pieces cut off and thrown into water 

 sink. When, however, the lungs are inflated, either artificially or by the efforts of a 

 iiruly born child to respire, they become inflated with air and are then buoyant in water ; 

 this is taken advantage of in medico-legal cases as a test to find out whether the child 

 has breathed or not. 



