70 F. W. THYNG 



The nasolacrimal duct (not shown in the reconstructions) 

 begins at the medial angle of the eye in an expanded end, dis- 

 connected from the ocular epithelium, and extends medially to 

 end near the epithelium of the meatus nasi inferior. It is a solid, 

 irregularly branching, cord of cells, entirely surrounded by mesen- 

 chyma. Outgrowths from the ocular extremity for the superior 

 and inferior lacrimal ducts have not developed. 



VASCULAR SYSTEM 



Heart ' 



The heart in its relation to the surrounding organs is shown 

 in plates 1 and 4. The section shown in plate 1 passes to the left 

 of the atrial and ventricular septa, and therefore, opens the left 

 atrium and ventricle. In plate 4 the section passes through the 

 cavities of the right side. The ventricular trabeculae are repre- 

 sented somewhat diagrammatically. 



The sinus venosus (S.v., pi. 4) receives the common hepatic 

 {V. hep.com.) and the right and left common cardinal veins 

 {Vv.card.c.d. and s.), and opens into the right atrium. 



Upon the dorsal wall of the right atrium {At.d., plate 4) is the 

 sagittally directed, sinu-atrial orifice. The latter forms a nar- 

 row slit, bounded laterally by the right and left sinus valves 

 {V.V.S.). The cephalic ends of the valves converge and meet in a 

 ridge. The continuation of this ridge, which can be traced for 

 some distance along the cephalic part of the interior of the atrium, 

 is the septum spurium. 



The caudal extremity of the left sinus valve meets the right 

 side of the septum primum at the caudal part of the right atrium. 

 Just where these two structures meet ventrally there is a ridge or 

 tubercle, which probably represents the caudal end of the future 

 septum secundum. Born ('89) goes into no detail with regard 

 to the earlier stages in the developm.ent of the septum secundum, 

 which is shown completely formed in his figure 29. From the 

 relation which the tubercle bears to the septum primum and the 

 left sinus valve it can scarcely be doubted that it would eventually . 

 form part of the adult limbus fossae ovalis. 



