GLOMUS COCCYGEUM. 



1355 



The arteries enter at the hilum, run in the trabeculoe, and branch freely. The smaller 

 arteries have a lymphoid sheath developed in their walls. This replaces the fibrous sheath which 

 the larger arteries receive from the trabeculae. Every here and there the lymphoid sheath 

 expands symmetrically or asymmetrically to form a lymphatic nodule (nodulus lymphaticus 

 lienalis). Many of the nodules thus formed are quite small ; others are visible to the naked eye 

 as white specks, but, however large or small they may be, each contains a network of capillaries. 

 Towards their termination the arteries lose their sheaths and become reduced to simple tubes of 

 endothelial cells ; gaps appear in their walls and finally the cells forming them become con- 

 tinuous with the reticulum cells of the pulp. The veins begin in the same way as the arteries 

 end. The pulp is, therefore, the modified capillary system of the spleen. 



Development. The spleen is mesodermal in origin. The first indication of its develop- 

 ment, in a 9-mm. embryo, is a thickening of the dorsal mesogastrium. In 10-12 mm. embryos 

 the ccelomic epithelium over the splenic rudiment is several layers thick. Soon the deeper 

 layers of the thickening are transformed into mesenchyme and the epithelium is reduced again 

 to a single layer. The first vascularisation of the spleen is effected by a capillary network. Out 

 of this the intra -splenic arteries and veins 

 differentiate. The undift'erentiated capil- 

 laries between them form capillary tufts 

 or spherules. These become transformed 

 into the pulp. The exact method of this 

 transformation is undetermined, but during 

 its progress great numbers of red blood 

 cells are produced. The lymphatic nodules 

 are developed in the later part of foetal 

 life, and with their contained lymphocytes 

 differentiate from the tunica adventitia of 

 the arteries. 



Arterial branches 



Accessory glomus - 



(ii.) GLOMUS COCCYGEUM. 



Accessory glomus -O 



The glomus coccygeum is a 

 small body, 2-2-5 mm. in diameter, 

 placed immediately anterior to the tip 

 of the coccyx, upon a branch of the 

 middle sacral artery. Usually it is Entrance of artery 



. n .. m ti into mam glomus 



accompanied by a group of smaller Accessory Q 



bodies of similar structure and arterial glomus 



relation. 



Accessory 

 glomus"" 



_ Arterial branches 



Accessory 

 ""glomus 



Structure. The glomus is enclosed 

 in a fibrous capsule and consists of round 

 or polyhedral cells with large nuclei lining 

 a considerable blood space, which is an 

 anastomosing channel between an artery 

 and a vein. 



Development. The glomus develops 

 from the capillary network of the region 

 of the tip of the embryonic taiL At first 

 the capillary walls differentiate as if to form an artery, then the cells of the middle coat, 

 instead of forming muscle, assume an epithelioid character. 



The position of the glomus coccygeum at the posterior end of the axis of the body, and the 

 fact that its blood-spaces form a wide arterio-venous anastomosis, suggest that it is a sort of 

 safety-valve on the peripheral circulation. No evidence that it produces an internal secretion 

 has, as yet, been obtained, and in spite of frequent statements' to the contrary it contains no 

 chromaphil cells (Stoerk). 



FIG. 1065. -SCHEMA OF THE RELATION PRESENTED BY THE 

 GLOMUS COCCYGEUM AND ITS ACCESSORY OUTLYING 



PARTS TO THE BRANCHES OF THE MIDDLE SACRAL 



ARTERY. (Reconstructed from serial sections through 

 the region.) From J. W. Thomson Walker. 



