184 TOPOGRAPHICAL ANATOMY OF THE 



conical part of the piriform lobe, and consists of a short stem from which 

 three branches — anterior, middle and posterior — usually radiate. In 

 the depths of the fissure, and most frequently partly or completely 

 hidden from view, are several short convolutions composing the iiisida. 



Bent round the middle or ascending branch of the Sylvian fissure is 

 a convolution bounded above by the ectosylvian sulcus (sulcus 

 ectosylvius). Above this is a convolution, generally complex in forma- 

 tion, limited dorsally by one of the deepest of the cerebral sulci, the 

 suprasylvian sulcus (sulcus suprasylvius), which is commonly connected 

 in front with the cruciate sulcus, and sometimes also with the orbital 

 sulcus. 



The area between the suprasylvian sulcus and the dorsal margin of 

 the hemisphere is indented by a longitudinal lateral sulcus (sulcus 

 lateralis). Between the suprasylvian and lateral sulci there is a subsid- 

 iary ectolateral sulcus (sulcus ectokteralis) that may be broken into 

 two or more segments. The lateral and suprasylvian sulci most 

 commonly extend over the occipital pole of the hemisphere to the 

 surface that is in contact with the tentorium cerebelli. 



Two other constant sulci, the orbital and the cruciate, are demon- 

 strable on the dorso- lateral surface of the hemisphere. The long, curved 

 orbital sulcus (sulcus orbitalis) begins not far from, or even in connec- 

 tion with, the anterior end of the suprasylvian sulcus, cuts the anterior 

 part of the hemisphere, and ends by joining the rhinal fissure. The 

 cruciate ^ sulcus (sulcus cruciatus) is of considerable depth and belongs 

 to both the medial and dorso-lateral surfaces of the hemisphere. Its 

 lateral end most commonly joins the suprasylvian sulcus. 



Medial Surface. — As has just been stated, the cruciate sulcus is pro- 

 longed round the margin of the hemisphere on to the medial surface, 

 where it joins a long, curved groove, roughly parallel to the corpus 

 callosum, that may possibly represent the combined intercalary and 

 calcarine- sulci (sulcus intercalaris : sulcus calcarinus) of the human 

 brain. Between this groove and the corpus callosum there is a long and 

 generally subdivided convolution that is considered by some to be the 

 homologue of the gyrus fornicatus of man. The callosal sulcus (sulcus 

 corporis callosi) separates the gyrus from the corpus callosum. 



If the specimen in which as much as possible of the brain-stem has 

 been removed be examined, the hippocampal fissure (fissura hippo- 

 campi) will be seen as a curved groove extending from the posterior end 

 of the callosal sulcus to the prominent part of the piriform lobe, of 

 which it forms the medial boundary. Along the convexity of the 



1 Crux [L], a cross. 



2 Calcar [L.], a spur. 



