268 



THE DUCTLESS GLANDS 



the thymus. In the ox, in addition to the four typical para- 

 thyroids, it is stated that there are accessory parathyroids 

 of macroscopic size in different regions of the neck and medias- 

 tinum. 



(k) In the Horse the relationships of the parathyroids have 



FIG. 72. 



FIG. 73. 



FIG. 74. 



FIG. 75. 



FIG. 76. 



FIGS. 72 to 76. Parathyroids in the guinea-pig. The extreme variability in 

 number and position is shown. In none of this series were any true 

 " internal " parathyroids seen with the unaided eye. 



not been fully ascertained. In a recent paper Estes states 

 that the external glandule of the horse is found in close relation 

 to the upper end of the thyroid or in the perithyroid areolar 

 tissue. The internal parathyroid is variously placed beneath 

 the capsule of the thyroid, usually near its upper pole. The 

 external gland i< much the larger. The horse then appears 



