262 THE VASCULAR SYSTEM. 



internally and above by the M. coccygeo-Uiacati, below and exter- 

 nally by the origin of the M. vastus externns, and below by the 

 M. pyrmnidalls. Each posterior heart is about two lines long and 

 one broad, with its long axis placed antero-posteriorly ; the outer 

 surface is uneven and appears to be unequally dilated. The lymph- 

 heart is closely attached to the surrounding parts, especially to 

 the fascia covering the M. ilii-coccygea, and posteriorly to the 

 M. levator aui and the M. pyramidalis. [The posterior lymph-hearts 

 receive lymph from the parts surrounding them, and from the 

 hinder extremities, and forward it into the V. lllaca connnunicaus. 



The posterior lymph-hearts are each supplied by a branch from 

 the corresponding coccygeal nerve (Waldeyer) by its dorsal branch. 

 The lymph-hearts are also in close connection with the sympathetic 

 system (Waldeyer).] 



PART IIL 



THE BLOOD, LYMPH, AND HISTOLOGY OF 



THE VESSELS. 



[The parts described in this section will be considered very 

 briefly, and only from an anatomical point of view, 



A. The blood ^ 



The blood varies in colour, according as it is obtained from an 

 artery or from a vein ; from an artery it has a bright red or scarlet 

 colour ; from a vein a darker shade : in the pulmonary vessels these 

 colours are reversed. The blood consists of a fluid plasma which 

 contains red and white corpuscles : the whole forming a slightly 

 alkaline, opaque, and somewhat sticky fluid. 



a. The plasma or liquor santjuinis is a transparent, clear, slightly 

 yellow fluid, faintly alkaline in reaction. 



^ Mr. Hurst has noticed a frog (R. teiiiporaria) iu which the blood was perfectly 

 colourless. 



